Mineral optik2 SKS teoriby:hill. gendoet hartonoSemester 3, 2009-2010Selasa, jam 09.50 10.40 jam 10.40 11.35

The Petrological Microscope

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The use of the Petrological Microscope

The use of the microscope allows us to examine rocks in much more detail. For example, it lets us :-

examine fine-grained rocks examine textures of rocks distinguish between minerals that are otherwise difficult to identify in hand-specimen (e.g. the feldspars)

Deer,W.A., Howie,R.A. & Zussman, J., 1978, An Introduction to the Rock Forming Minerals, Longman Group Ltd., London, 528 p. Philpotts A.R., 1989, Petrografi of Igneous and Metamorphic Rocks, Prentice-Hall, Inc, Engewood Cliffs, New Jersey, 179 p. Williams, Turner, F,J. & Gilbert, C.M., 1954, Petrography : An Introduction to the Study of Rocks in Thin Sections, W.H. Freeman & Co., San Francisco, 406 p.Hatch, F.H; Wells, A.K., & Wells, M.K., 1972, Petrology of the Igneous Rocks, George Allen & Unwin (Publishers) Ltd., 13 Ed. 551 p. Jones, N.W., & Bloss, F.D., 1980, Laboratory Manual For Optical Mineralogy, Burgess Publishing Company. Pustaka

A petrological microscope

The petrological microscopediffers from an ordinary microscope in two ways:

it uses polarised lightand the stage rotates

There are two sheets of polaroid: the one below the stage of the microscope is the polariser, the other, above the stage, is the analyser. The analyser can be moved in and out.

Most rocks cut and ground to a thickness of 0.03mm become transparent.

lenseyepiecefocuslight sourceanalyserpolariserrotating stagefine focus

Preparing thin sections

Rock specimens are collected in the field, then cut into smallthin slabs. These are glued on to glass slides and grounddown to 0.03mm thickness. At this thickness all rocksbecome transparent. Only a few minerals, mainly oreminerals, remain opaque, i.e. stay black under PPL.

If the sections are too thick, the polarisation colours areaffected. Quartz is used to check thickness for this reason see the next slide

The colours appear in a series of repeated rainbows across the chart and amineral may show any colour up to a maximum, reading from the left.quartzfeldsparcalciteolivineamphibolepyroxenebiotite muscoviteRead along 0.03mm line to the highest order colour seen in the mineralRead along diagonal to top for mineral name

Identifying MINERALS in thin section

When a slide is examined under the microscope, it is important to identify any mineral properties under plane polarised light (PPL) first (analyser out); then proceed to crossed polars (XPL) where the two polaroid sheets are at right angles to each other (analyser in).

Mineral properties under PPL

colour (natural colour)transparency (clear, cloudy or opaque)relief (high or low)crystal or fragment shapecleavage fracturepleochroism (colour change when stage is rotated)

1) Light passes through the lower polarizerUnpolarized light Jane Selverstone, University of New Mexico, 2003

2) Insert the upper polarizerwest (left)east (right)Now what happens?What reaches your eye?Why would anyone design a microscope that prevents light from reaching your eye???XPL=crossed nicols (crossed polars) Jane Selverstone, University of New Mexico, 2003

Note how the olivine with its high relief stands out from the surrounding low relief plagioclaseRELIEFPPLplagioclaseolivine

Mineral properties in PPL: relief Relief is a measure of the relative difference in n between a mineral grain and its surroundings Relief is determined visually, in PPL Relief is used to estimate ngarnet:n = 1.72-1.89quartz:n = 1.54-1.55epoxy:n = 1.54Quartz has low reliefGarnet has high relief

Mineral properties in PPL: relief Relief is a measure of the relative difference in n between a mineral grain and its surroundings Relief is determined visually, in PPL Relief is used to estimate n Jane Selverstone, University of New Mexico, 2003

What causes relief?Difference in speed of light (n) in different materials causes refraction of light rays, which can lead to focusing or defocusing of grain edges relative to their surroundings Jane Selverstone, University of New Mexico, 2003

Two sets of cleavage are seen in this amphibole crystal; note the 120o angle between the cleavagesCLEAVAGEPPLamphibole1st set run parallel to line2nd set of cleavage

The olivine here shows uneven fractures which appear dark grey in the crystalFRACTUREPPLolivine

The biotite shows its distinct brown shades under PPL against the clear colourless quartz and feldsparCOLOURPPLbiotiteamphibole

PLEOCHROISMTwo views under PPL showing colour change in biotite on rotating the stage.

PPLbiotiterotated 90o

Mineral properties under XPL

interference colours (under XPL the colours seen are not the natural colours of the mineral but those caused by the interference of two refracted beams of light passing through an anisotropic mineral ; they are called interference colours)extinction angle (as the stage is rotated, each anisotropic mineral goes extinct every 90o; in cases where there is cleavage in the mineral it is possible to measure the angle of extinction relative to the crosswires)twinning (may be seen in coloured minerals under PPL, but most obvious under XPL, especially with regard to the feldspars)

Now insert a thin section of a rock in XPLwest (left)east (right)Light vibrating E-WHow does this work??Unpolarized lightnorthsouth Jane Selverstone, University of New Mexico, 2003

Conclusion has to be that minerals somehow reorient the planes in which light is vibrating; some light passes through the upper polarizerBut, note that some minerals are better magicians than others (i.e., some grains stay dark and thus cant be reorienting light)olivineplagPPLXPL

Interference colourswhite/grey/black in quartz, microcline and plagioclasemuch brighter colours of ferro-magnesian minerals including amphibole, pyroxene, olivinepearly grey shades of calcitequartzamphibolecalcite

Liquids, gases, amorphous solids such as glass, and isotropic minerals (isometric crystal system) stay black in all orientationsReview: With any isotropic substance (spherical indicatrix), when the analyzer is inserted (= crossed-nicols or XPL) no light passes extinct, even when the stage is rotatedNote: the gray field should also be extinct (glass and epoxy of the thin section are also isotropic), but is left lighter for illustration

Rotating the stage

Anisotropic minerals with an elliptical indicatrix section change color as the stage is rotated; these grains go black 4 times in 360 rotation-exactly every 90o

Consider rotating the crystal as you watch:B = polarizer vibration direction parallel e only E-ray Analyzer in extinct

C = polarizer vibration direction || w only O-ray also extinct with analyzerewwe

Materials Science C

Optical propertiesBased on: B.S. Mitchell, An introduction to materials engineering and science for chemical and materials engineerspp644-659

Optical devicesExamples: mirrors, lenses, beamsplitters, photovoltaic devices

Optical Properties of MaterialsInteraction of electromagentic radiation (light) with a material

Absorption Reflection Transmission A material cannot simultaneously be highly absorptive, reflective and transmissiveAbsorptivityReflectivityTransmissivity

Optical Properties of Metals and AlloysShininess and inability to transmit visible light indicates high absorption high reflectionlinear absorption coefficient (up to R = 1) and R determine how light interacts with a material

Reflectance and color

Reflectance and color- Surface texture

Photoelectric effectRelease of electrons due to absorption of light energy potential energy barrier for surface electrons is finite critical energy for release: = W - Ef = h c below c: no ejection of photoelectrons characteristic measure

Photoelectric effectPhotoelectric emission depending on wavelength optimal emission at c below c: insufficient energy above c : decrease of electronic excitations efficiency

Electromagnetic spectrum

Optical Properties of ceramics and glassesRefractive index n velocity of light in vacuum: c = 299 792 458 m/s velocity of light in any other medium: v (v < c) refractive index n = c/v

Refractive indexValues between 1 and 4 air: 1.003 silicate glasses: 1.5 to 1.9 solid oxide ceramics: 2.7Dependent on structure-type and packing geometry glasses and cubic crystals: n is independent of direction other crystal systems: n larger in closed-packed directions SiO2: glass = 1.46, tridymite = 1.47, cristobaltite = 1.49 quartz = 1.55

Cristalline silicate vs glassTEM images Addition of large ions (Pb, Ba) toSiO2 structures increases n significantly

Refractive indexMechanical distortions of isotopic glasses changes n tensile stress: lower n normal to direction of applied stress compression: higher n normal to direction of applied stress

Reflection and refractionn can be expressed with the angles of incidence and refraction

Absorbance and color

Absorbance and colorAbsorption of certain wavelength results in colorGenerating color in ceramics:Addition of transition elements with incomplete d band fillingV, Cr, Mn, Fe, Co, Ni

Light scattering in solidsSome inherently transparent materials appear milky: translucencyScattering Pores (npore < nsolid)- second-phase particles (SnO2) (n2nd phase > nsolid)

SummaryAbsorption, Transmission, ReflectionOrigin of colors in metals and ceramicsRefractive indexLight scattering

Optical MineralogyOptical MineralogyUse of the petrographic microscope John Winter, Whitman College with some slides Jane Selverstone, University of New Mexico, 2003

Why use the microscope??Identify minerals (no guessing!)Determine rock typeDetermine crystallization sequenceDocument deformation historyObserve frozen-in reactionsConstrain P-T historyNote weathering/alteration Jane Selverstone, University of New Mexico, 2003

The petrographic microscopeAlso called a polarizing microscopeIn order to use the scope, we need to understand a little about the physics of light, and then learn some tools and tricks Jane Selverstone, University of New Mexico, 2003

What happens as light moves through the scope?Frequency = # of waves/sec to pass a given point (hz)f = v/l v = velocity(in physics v = c, but no longer) Jane Selverstone, University of New Mexico, 2003

Electromagnetic spectrum & visible portionViolet (400 nm) Red (700 nm)White = ROYGBV

(can be separated by dispersion in a prism)

RefractionIncident ray and reflected ray:1) of incidence i = of reflection r'2) coplanar plane of incidence(^ plane of interface)

Refracted ray: 1) Slower in water (or glass) 2) r iDepends on D velocityIncidentReflectedairRefractedwaterirr

For a substance x:nx = vair/vxnair = ?? light is slower in water, glass, crystalsIs nwater greater or less than 1??Larger n associated with slower V !!Snells Law: ni sin i = nr sin rfor 2 known media (air/water) sin i/sin r = nr / ni = constSo can predict angle change (or use to determine nr)Index of refraction

Light beam = numerous photons, each vibrating in a different planeVibration in all directions ~ perpendicular to propagation directionvibration directionspropagation directionWhat happens as light moves through the scope?Polarized LightUnpolarized LightEach photon vibrates as a wave form in a single planeLight beam = numerous photons, all vibrating in the same planeplanes of vibration

1) Light passes through the lower polarizerUnpolarized light Jane Selverstone, University of New Mexico, 2003

2) Insert the upper polarizerwest (left)east (right)Now what happens?What reaches your eye?Why would anyone design a microscope that prevents light from reaching your eye???XPL=crossed nicols (crossed polars) Jane Selverstone, University of New Mexico, 2003

The Optical IndicatrixShows how ni varies with vibration direction.Vectors radiating from centerLength of each proportional to ni for light vibrating in the direction of the vectorIndicatrix = surface connecting tips of vectors (a representational construct only!)Isotropic media have all ni the same (by definition)What is the shape of an isotropic indicatrix? Amorphous materials or isometric crystals are (optically) isotropic with a spherical indicatrix

The Isotropic IndicatrixA section through the center of an indicatrix all n for light propagating ^ the sectionConventions:1) Indicatrix w/ center on interface surface2) n (radial vectors of circular section in this case) same in all possible vibration directionsIncoming light can (and will) vibrate in the same direction(s) it did prior to entryIf unpolarized, it will remain so.Only effect is slower velocity (rep. by closer symbol spacing)

Liquids, gases, amorphous solids such as glass, and isotropic minerals (isometric crystal system) stay black in all orientationsReview: With any isotropic substance (spherical indicatrix), when the analyzer is inserted (= crossed-nicols or XPL) no light passes extinct, even when the stage is rotatedNote: the gray field should also be extinct (glass and epoxy of the thin section are also isotropic), but is left lighter for illustration

Mineral properties in PPL: relief Relief is a measure of the relative difference in n between a mineral grain and its surroundings Relief is determined visually, in PPL Relief is used to estimate ngarnet:n = 1.72-1.89quartz:n = 1.54-1.55epoxy:n = 1.54Quartz has low reliefGarnet has high relief

Mineral properties in PPL: relief Relief is a measure of the relative difference in n between a mineral grain and its surroundings Relief is determined visually, in PPL Relief is used to estimate n Jane Selverstone, University of New Mexico, 2003

What causes relief?Difference in speed of light (n) in different materials causes refraction of light rays, which can lead to focusing or defocusing of grain edges relative to their surroundings Jane Selverstone, University of New Mexico, 2003

Now insert a thin section of a rock in XPLwest (left)east (right)Light vibrating E-WHow does this work??Unpolarized lightnorthsouth Jane Selverstone, University of New Mexico, 2003

Conclusion has to be that minerals somehow reorient the planes in which light is vibrating; some light passes through the upper polarizerBut, note that some minerals are better magicians than others (i.e., some grains stay dark and thus cant be reorienting light)olivineplagPPLXPL

Fig 6-7 Bloss, Optical Crystallography, MSAAnisotropic crystalsCalcite experiment and double refractionO-ray (Ordinary) Obeys Snell's Law and goes straightVibrates ^ plane containing ray and c-axis (optic axis)E-ray (Extraordinary)deflectedVibrates in plane containing ray and c-axis..also doesn't vibrate ^ propagation, but we'll ignore this as we said earlier

Both rays vibrate parallel to the incident surface for normal incident light, so the interface x-section of the indicatrix is still valid, even for the E-rayThus our simplification of vibration ^ propagation works well enoughFrom now on we'll treat these two rays as collinear, but not interacting, because it's the vibration direction that countsFig 6-7 Bloss, Optical Crystallography, MSAIMPORTANT: A given ray of incoming light is restricted to only 2 (mutually perpendicular) vibration directions once it enters an anisotropic crystalCalled privileged directionsEach ray has a different nw = noe = nE in the case of calcite w < e which makes the O-ray dot appear above E-ray dot

Some generalizations and vocabularyAmorphous materials and isometric minerals (e.g., garnet) are isotropic they cannot reorient light. These minerals are always extinct in crossed polars (XPL).All other minerals are anisotropic they are all capable of reorienting light (acting as magicians).All anisotropic minerals contain one or two special propagation directions that do not reorient light.Minerals with one special direction are called uniaxialMinerals with two special directions are called biaxial Jane Selverstone, University of New Mexico, 2003

n > 1 for anisotropic substancesn = f(vibration direction) Indicatrix no longer a sphereIndicatrix = ellipsoid Note: continuous function, smooth ellipsoid.Hexagonal and tetragonal crystals have one unique crystallographic axis (c axis) ^ 2 identical ones The optical properties reflect this as well: ellipsoid of rotation about c (optically uniaxial) and c = the optic axis

Uniaxial ellipsoid and conventions:Fig 6-11 Bloss, Optical Crystallography, MSA

Circular Section^ optic axis: all w'sPrincipal Sections have w and true e: max & min n'sRandom Sections (e' and w) All sections have w!!

Any non-circular cut through the center of a uniaxial indicatrix will have w as one semiaxis and e' (or true e) as the otherDepending on light propagation we can have:

Fig 6-7 Bloss, Optical Crystallography, MSAFig 6-8 Bloss, Optical Crystallography, MSACalcite experiment and double refraction

Circular Section: all rays are O-rays and vibrate parallel w

Random Section: O-ray vibrates parallel w E-ray vibrates parallel e'Fig 6-13 Bloss, Optical Crystallography, MSA

Principal section:This is essentially the same as random, but here e' is really true e.In this case both rays really do vibrate ^ propagation & follow same path (as we have simplified the random case)We shall consider random and principal as alike, only the value of e varies.Fig 6-13 Bloss, Optical Crystallography, MSA

Essentially 2 possibilities(light coming toward you)1. Circular sectionLight prop. || OAAll vibration directions ^c are the same nOptic AxisFig 6-13 Bloss, Optical Crystallography, MSALike isotropic(no unique plane containing ray and c-axis)Only one ray (O-ray) with n = w (doesnt split to two rays)Extinct with analyzer in and stays that way as rotate stage (behaves as though isotropic)If incident light is unpolarized it will remain so

Essentially 2 possibilities(light coming toward you)2 raysOnly 2 privileged vibration directionsO-ray with n = wE-ray with n = e or e (depending on section)Does not stay same as rotate (more later)2. Elliptical sectionAny orientation other than circular

B-C: Polarized parallel e and wTransmits only one ray! (no component parallel to the other privileged direction) Note convention here: Light slows upon entering xl. Since frequency (& color) is about same, the slowing is illustrated by more compressed wave forms (they spend more time in the xl), so vibrate more times (vibrate more per length traveled) A: Unpolarized Ray splits into e and wThis figure rotates the light source(we rotate the crystal)Fig 6-17 Bloss, Optical Crystallography, MSA

D: Polarized at random angle

Resolves into components parallel e and parallel w

Rotating the stage

Anisotropic minerals with an elliptical indicatrix section change color as the stage is rotated; these grains go black 4 times in 360 rotation-exactly every 90o

Consider rotating the crystal as you watch:B = polarizer vibration direction parallel e only E-ray Analyzer in extinct

C = polarizer vibration direction || w only O-ray also extinct with analyzerewwe

Consider rotating the crystal as you watch:

DPolarized light has a component of eachSplits two raysone is O-ray with n = wother is E-ray with n = eWhen the rays exit the crystal they recombine

ew

REVIEWCalcite: Fig 6-72 rays, each polarizedvibrate ^ each other & in plane of incidence Indicatrix- uniaxialRandom SectionO-ray vibrates parallel wE-ray vibrates parallel e'Principal sectionCircular sectione' and w = privileged vibration directions

InterferenceA: Particles in phase if displaced from rest position by same amount in same directiona1 - a2 - a3 are all in phaseb1 - b2 - b3 are also all in phase (but not with a1)particles perfectly out of phase: equal-but-opposite displacementb1 and c1 are not, since in an instant it won't workFig 7-1 Bloss, Optical Crystallography, MSAPath Difference (D) = distance between any 2 points on a wave formusually expressed as xlD between any 2 points in phase = il (i=any integer)D between any 2 points perf. out of phase = ((2i+1)/2) l

B: Instant later with a second ray enteringC: Shows algebraic sum interference composite rayIf both waves in phase constructive interference with amplitude greater than either (intensity = A2)

InterferenceInterference of light polarized in perpendicular planesThis works in air & isotropic media, but not in crystals where vibrate independentlyNow we're ready for a big step

InterferencePlane polarized light enters xl. & resolved into 2 rays (if not || optic axis), which vibrate ^ each other & travel at different velocities (since have different n)Will thus travel diff # of l (even if frequency same or similar)So if in phase when enter, won't be when exit!!The path diff (D) between O-ray and E-ray = t (|w-e'|) (t = thickness)absolute value because the crystal can be (+) or (-)D then = t(N-n) and each mineral has a ~unique w and e, D is thus a function of the thickness, the mineral observed, and the orientation

Interference2 crystals of equal t, but different Dni A: n = 1/2 Nn=small ref index N=large " "slow ray requires 2 periods & fast only onethus come out polarized in same plane as entered no transmission by analyzer in XPL

Interference2 crystals of equal t, but different Dni B: n = 3/4 NSlow ray requires 2 periods & fast 1.5 100% transmission by analyzer in XPL

Transmission by the AnalyzerDetermined by:a) Angle between analyzer and polarizer (fixed at 90o)b) Angle between polarizer and closest privileged direction of xlWhen polarizer || either privileged vibration direction extinct, since only one ray & it's cancelledEvery crystal goes extinct 4 times in 360o rotation (unless isotropic)

Transmission by the Analyzerc) D = path difference = t (N-n) Fig. 7-4 t(N-n) = 1l 0% transmissiont(N-n) = 1.5l 100% transmission

Transmission by the AnalyzerDetermined by:d) l of lighta new conceptin part (c) D has been expressed in terms of l...but it's really an absolute retardation, some finite # of nm (or A or miles)If the transmitted light is white (mixed), each wavelength will be retarded t(N-n) by the same absolute distance, which will be a different x/l

Transmission by the AnalyzerExample: assume xl has t(N-n) that will retard D = 550 mm & viewed 45o off extinction (max intensity)

retardation 550550550550550550selected light l 40044048955062973313/8 l11/4 l11/8 l1 l7/8 l3/4 lYou can see 550 mm gets no transmission & others varying amount

retardation 550550550550550550selected light l 400440489550629733 13/8 l 11/4 l 11/8 l 1 l7/8 l3/4 l Fig 7-7 Bloss, Optical Crystallography, MSA

retardation 800800800800800800 800selected light l 400426457550581711 800 2 l 17/8 l 13/4 l 11/2 l 7/8 l1 1/8 l 1 l Fig 7-7 Bloss, Optical Crystallography, MSA

Color chart Colors one observes when polars are crossed (XPL) Color can be quantified numerically: d = nhigh - nlow

Color chartShows the relationship between retardation, crystal thickness, and interference color550 mm red violet800 mm green1100 mm red-violet again (note repeat )0-550 mm = 1st order 550-1100 mm = 2nd order 1100-1650 mm = 3rd order...Higher orders are more pastel

1) Find the crystal of interest showing the highest colors (D depends on orientation)2) Go to color chartthickness = 30 micronsuse 30 micron line + color, follow radial line through intersection to margin & read birefringenceSuppose you have a mineral with second-order greenWhat about third order yellow?Estimating birefringence

Example: Quartz w = 1.544 e = 1.553Data from Deer et al Rock Forming MineralsJohn Wiley & Sons

Example: Quartz w = 1.544 e = 1.553Sign?? (+) because e > w e - w = 0.009 called the birefringence (d) = maximum interference color (when seen?)What color is this?? Use your chart.

Color chart Colors one observes when polars are crossed (XPL) Color can be quantified numerically: d = nhigh - nlow

Example: Quartz w = 1.544 e = 1.553Sign?? (+) because e > w e - w = 0.009 called the birefringence (d) = maximum interference color (when see this?)What color is this?? Use your chart.For other orientations get e' - w progressively lower colorRotation of the stage changes the intensity, but not the hueExtinct when either privileged direction N-S (every 90o) and maximum interference color brightness at 45o360o rotation 4 extinction positions exactly 90o apart

So far, all of this has been orthoscopic (the normal way)All light rays are ~ parallel and vertical as they pass through the crystalOrthoscopic viewingFig 7-11 Bloss, Optical Crystallography, MSAxl has particular interference color = f(biref, t, orientation)Points of equal thickness will have the same color isochromes = lines connecting points of equal interference colorAt thinner spots and toward edges will show a lower color Count isochromes (inward from thin edge) to determine order

If this were the maximum interference color seen, what is the birefringence of the mineral?

Conoscopic ViewingA condensing lens below the stage and a Bertrand lens above itArrangement essentially folds planes of Fig 7-11 coneLight rays are refracted by condensing lens & pass through crystal in different directionsThus different propertiesOnly light in the center of field of view is vertical & like ortho Interference Figures Very useful for determining optical properties of xlFig 7-13 Bloss, Optical Crystallography, MSA

How interference figures work (uniaxial example)BertrandlensSample(looking down OA)sub-stagecondenserConverging lenses force light rays to follow different paths through the indicatrixWE-W polarizerN-S polarizerWhat do we see?? Jane Selverstone, University of New Mexico, 2003

Uniaxial Interference FigureCircles of isochromesNote vibration directions: w tangential e' radial & variable magnitudeBlack cross (isogyres) results from locus of extinction directionsCenter of cross (melatope) represents optic axisApprox 30o inclination of OA will put it at margin of field of view

Uniaxial FigureCentered axis figure as 7-14: when rotate stage cross does not rotateOff center: cross still E-W and N-S, but melatope rotates around centerMelatope outside field: bars sweep through, but always N-S or E-W at centerFlash Figure: OA in plane of stage Diffuse black fills field brief time as rotate

Accessory PlatesWe use an insertable 1-order red (gypsum) plate

Accessory PlatesWe use an insertable 1-order red (gypsum) plateSlow direction is marked N on plateFast direction (n) || axis of plateThe gypsum crystal is oriented and cut so that D = (N-n) 550nm retardation it thus has the effect of retarding the N ray 550 nm behind the n rayIf insert with no crystal on the stage 1-order red in whole field of viewFig 8-1 Bloss, Optical Crystallography, MSA

Accessory PlatesSuppose we view an anisotropic crystal with D = 100 nm (1-order gray) at 45o from extinctionIf Ngyp || Nxl AdditionRay in crystal || Ngyp already behind by 100nm & it gets further retarded by 550nm in the gypsum plate100 + 550 650nmWhat color (on your color chart) will result?Original 1o grey 2o blue

Accessory PlatesNow rotate the microscope stage and crystal 90o Ngyp || nxl (D still = 100 nm)Ngyp || nxl Subtraction Ray in the crystal that is parallel to Ngyp is ahead by 100nm 550mm retardation in gypsum plate 450nm behindWhat color will result?1o orange

What will happen when you insert the gypsum plate?

What will happen when you insert the gypsum plate?

Optic Sign DeterminationFor all xls remember e' vibrates in plane of ray and OA, w vibrates normal to plane of ray and OA1) Find a crystal in which the optic axis (OA) is vertical (normal to the stage). How would you do that?2) Go to high power, insert condensing and Bertrand lenses to optic axis interference figure(+) crystal: e > w so w faster

Fig 7-13 Bloss, Optical Crystallography, MSA

Optic Sign DeterminationInserting plate for a (+) crystal: subtraction in NW & SE where n||N addition in NE & SW where N||NWhole NE (& SW) quads add 550nmisochromes shift up 1 orderIsogyre adds redIn NW & SE where subtractEach isochrome loses an order Near isogyre (~100nm) get 450 yellow in NW & SE (100-550)and 650 blue in NE & SW (100+550)(+) crystal: e > w so w fasteraddaddsubsub

(+) OA Figure with plateYellow in NW is (+)(+) OA Figure without plate

Optic Sign DeterminationInserting plate for a (-) crystal: subtraction in NE & SW where n||N addition in NW & SE where N||NWhole NW (& SE) quads add 550nmisochromes shift up 1 orderIsogyre still adds redIn NE & SW where subtractEach isochrome loses an order Near isogyre (~100nm) get 650 blue in NW & SE and 450 yellow in NE & SW(-) crystal: e < w so w sloweraddsubaddsub

(-) OA Figure with plateBlue in NW is (-)(-) OA Figure without plate(same as (+) figure)

Can determine the refractive index of a mineral by crushing a bit up and immersing the grains in a series of oils of known refractive index.When the crystal disappears perfectly nmineral = noilThe trick is to isolate w and true e by getting each E-W (parallel to the polarized light)Orienting crystals to determine w and e

To measure w only (if all grains of a single mineral):1) Find a grain with low interference colors- ideally a grain that remains extinct as the stage is rotated2) (check for centered OA figure)3) Determine optic sign while you're at it (for use later)4) Back to orthoscopic : all rays are w 5) Compare nxl to noilOrienting crystals to determine w and e

Now look at the other crystals of the same mineral:If the crystals are randomly oriented in a slide or thin section you may see any interference color from gray-black (OA vertical) to the highest color possible for that mineral (OA in plane of stage and see w and true e). Orienting crystals to determine w and e

To measure e :1) Find a grain with maximum interference colors2) (Check for flash figure?)3) Return orthoscopic at lower power4) Rotate 45o from extinction (either direction)

5) Figure out whether e is NE-SW or NW-SE & rotate it to E-W extinction6) Then only e coming through!Oils are then used nmust redo with each new oil as get closer! Ugh!Orienting crystals to determine w and e

Changes in absorption color in PPL as rotate stage (common in biotite, amphibole)Pleochroic formula:Example: Tourmaline: e = dark green to bluish w = colorless to tanCan determine this as just described by isolating first w and then e E-W and observing the colorPleochroism

Hornblende as stage is rotated

Biotite as stage is rotated

Biaxial CrystalsOrthorhombic, Monoclinic, and Triclinic crystals don't have 2 or more identical crystal axesThe indicatrix is a general ellipsoid with three unequal, mutually perpendicular axesOne is the smallest possible n and one the largest a = smallest n(fastest) b = intermediate n g = largest n(slowest)

The principal vibration directions are x, y, and z ( x || a, y || b, z || g)

By definition a < a' < b < g '< gFig 10-1 Bloss, Optical Crystallography, MSA

Biaxial CrystalsIf a < b < g then there must be some point between a & g with n = bBecause = b in plane, and true b is normal to plane, then the section containing both is a circular sectionHas all of the properties of a circular section! If look down it:all rays = bno preferred vibration directionpolarized incoming light will remain sounpolarized thus appear isotropic as rotate stagegaLooking down true b= b

Biaxial CrystalsIf a < b < g then there must be some point between a & g with n = bgaLooking down true b= b^ optic axis by definitionOA

Biaxial CrystalsIf a < b < g then there must be some point between a & g with n = b^ optic axis by definition

And there must be two! Biaxial

Orthorhombic, Monoclinic, and Triclinic minerals are thus biaxial and Hexagonal and tetragonal minerals are uniaxial

Biaxial CrystalsNomenclature:2 circular sections 2 optic axes Must be in a-g plane = Optic Axial Plane (OAP)Y || b direction ^ OAP = optic normalFig 10-2 Bloss, Optical Crystallography, MSAAcute angle between OA's = 2VThe axis that bisects acute angle = acute bisectrix = Bxa The axis that bisects obtuse angle = obtuse bisectrix = Bxo

Biaxial CrystalsB(+) defined as Z (g) = Bxa Thus b closer to a than to g

Biaxial CrystalsB(-) defined as X (a) = Bxa Thus b closer to g than to agaLooking down true b= b= bOAOA

Let's see what happens to unpolarized light travelling in various directions through a biaxial crystal Light will propagate with normal incidence to:Both = O-raysBoth polarized, and vibrate ^ each other (as uniaxial)One ray vibrates || Z and has n = g and the other vibrates || Y and n = b...or Z and X or Y and X1) Principal Plane - Includes 2 of the 3 true axes or principal vibration directions

Let's see what happens to unpolarized light travelling in various directions through a biaxial crystal Light will propagate with normal incidence to:This is identical to uniaxial:1 O-ray and 1 E-ray g and a' or b and g' ... vibration in incident plane so indicatrix works!2) Semi-random Plane Includes one principal vibration direction

Vibration directions of 2 rays in all 3 cases are mutually perpendicular, and || to the longest and shortest axes of the indicatrix ellipse cut by the incident planeThis is the same as with uniaxial, only the names change3) Random Plane No principal vibration directions 2 E-rays One vibrates in the OWZ' plane and || OZ with n = g' The other vibrates in the OWX' plane and || OX with n = a

4) Circular Section (either one)Acts as any circular section:Unpolarized remains soPolarized will pass through polarized in the same direction as entered with n = b extinct in XPL and remains so as rotate stage

ReviewFig 10-10 Bloss, Optical Crystallography, MSA

Biaxial Interference FiguresBxa figure (Bxa is vertical on stage)As in uniaxial, condensing lens causes rays to emanate out from OOX OS OA results in decreasing retardation (color) as g bOA OT OUIncrease again, but now because b aOX OQ OP incr retardation (interference colors)OR is random with a' and g'Fig 10-14 Bloss, Optical Crystallography, MSA

Biaxial Interference FiguresBxa figure

Result is this pattern of isochromes for biaxial crystalsFig 10-15 Bloss, Optical Crystallography, MSA

Biaxial Interference FiguresBiot-Fresnel Rule: for determining privileged vibration directions of any light ray from path and optic axesCalcite Expt: no longer a single plane containing ray and OAVibration directions bisect angle of planes as shown

Biaxial Interference FiguresApplication of B-F rule to conoscopic view Bxa figure+ = bisectrices of optic axis planes Isogyres are locus of all N-S (& E-W) vibration directionsSince incoming light vibrates E-W, there will be no N-S component extinctFig 10-16 Bloss, Optical Crystallography, MSA

Biaxial Interference FiguresCentered Bxa FigureFig 10-16 Bloss, Optical Crystallography, MSA

Biaxial Interference FiguresSame figure rotated 45oOptic axes are now E-WClearly isogyres must swingDemonstration

As rotate Centered Optic Axis Figure Large 2V:

Bxa Figure with Small 2V:Not much curvatureMakes use of Bxa awful

Always use optic axis figuresEasiest to find anyway. Why?Bxo looks like Bxa with 2V > 90oRandom Figures: Isogyre sweeps through field (not parallel x-hair at intersection, so can recognize from uniaxial even with this odd direction)Useless if far from OA

Biaxial Optic SignB(-)a = Bxa thus b closer to gaddaddsubtract100 gray + 550 650 blue100 gray - 550 450 yellow

Biaxial Optic SignB(-) a = Bxa thus b closer to g (in stage)Centered Bxa 2V = 35oCentered Bxa 2V = 35oWith accessory plate

Biaxial Optic SignB(+) g = Bxa thus b closer to a (in stage)subsubadd

Always use Optic Axis Figure & curvature of isogyre to determine optic signHow find a crystal for this?Blue in NW is (-) still works

Estimating 2VOAPFig 11-5A Bloss, Optical Crystallography, MSA

Sign of ElongationgIf g || elongation will always add length slowIf a || elongation will always subtract length fastU(+) will also length slowU(-) will also length fasta

Sign of ElongationbIf b || elongationSometimes will add length slowSometimes will subtract length fastgba

Optical Mineralogy in a NutshellUse of the petrographic microscope in three easy lessonsPart II Jane Selverstone, University of New Mexico, 2003

Quick review Isotropic minerals velocity changes as light enters mineral, but then is the same in all directions thru xtl; no rotation or splitting of light. Anisotropic minerals light entering xtls is split and reoriented into two plane-polarized components that vibrate perpendicular to one another and travel w/ different speeds.Uniaxial minerals have one special direction along which light is not reoriented; characterized by 2 RIs.Biaxial minerals have two special directions along which light is not reoriented; characterized by 3 RIs.These minerals are characterized by a single RI (because light travels w/ same speed throughout xtl)

Weve talked about minerals as magicians - now lets prove it!

single light ray coming into cc is split into two rays are refracted different amounts rays have different velocities, hence different RIs stationary ray=ordinary, rotating ray=extraordinary because refraction of e is so large, cc must have hi d (remember: d = nhi - nlo)

Conclusions from calcite experimentIf we were to look straight down c-axis, we would see only one star no splitting!

Back to birefringence/interference colorsObservation: frequency of light remains unchanged during splitting, regardless of materialF= V/l if light speed changes, l must also changel is related to color; if l changes, color also changes

Light waves may be in phase or out of phase when they exit xtl

When out of phase, some component of light gets through upper polarizer and displays an interference color

When one of the vibration directions is parallel to the lower polarizer, no light gets through the upper polarizer and the grain is at extinction (=black)Interference phenomenaSee Nesse p. 41, 46-48

At time t, when slow ray 1st exits xtl:Slow ray has traveled distance dFast ray has traveled distance d+Dtime = distance/rateSlow ray:t = d/Vslow

Fast ray: t= d/Vfast + D/Vair

Therefore: d/Vslow = d/Vfast + D/Vair

D = d(Vair/Vslow - Vair/Vfast)

D = d(nslow - nfast)

D = d d

D = thickness of t.s. x birefringence

Birefringence/interference colorsRetardation in nanometersThickness in micronsbirefringence

Remember determining optic sign last week with the gypsum plate?

Lets look at interference colors in a natural thin section:Different grains of same mineral are in different orientations

Time for some new tricks: the optical indicatrixThought experiment:Consider an isotropic mineral (e.g., garnet)What geometric shape is defined by mapped light rays?

Isotropic indicatrixSoccer ball(or an orange)

anisotropic minerals - uniaxial indicatrixquartzcalcitec-axisc-axis

Uniaxial indicatrixc-axisc-axisSpaghetti squash = uniaxial (+)tangerine = uniaxial (-)quartzcalcite

Circular section is perpendicular to the stem (c-axis)Uniaxial indicatrix

Uniaxial indicatrix(biaxial ellipsoid)What can the indicatrix tell us about optical properties of individual grains?

Propagate light along the c-axis, note what happens to it in plane of thin section

Grain changes color upon rotation. Grain will go black whenever indicatrix axis is E-W or N-S This orientation will show the maximum d of the mineralne - nw > 0therefore, d > 0Now propagate light perpendicular to c-axis

anisotropic minerals - biaxial indicatrixclinopyroxenefeldsparNow things get a lot more complicated

Biaxial indicatrix(triaxial ellipsoid)There are 2 different ways to cut this and get a circle

Alas, the potato (indicatrix) can have any orientation within a biaxial mineralolivineaugite

but there are a few generalizations that we can makeThe potato has 3 perpendicular principal axes of different length thus, we need 3 different RIs to describe a biaxial mineralX direction = na (lowest)Y direction = nb (intermed; radius of circ. section)Z direction = ng (highest) Orthorhombic: axes of indicatrix coincide w/ xtl axes Monoclinic: Y axis coincides w/ one xtl axis Triclinic: none of the indicatrix axes coincide w/ xtl axes

2V: a diagnostic property of biaxial minerals When 2V is acute about Z: (+) When 2V is acute about X: (-) When 2V=90, sign is indeterminate When 2V=0, mineral is uniaxial2V is measured using an interference figure More in a few minutes

How interference figures work (uniaxial example)BertrandlensSample(looking down OA)substagecondensorConverging lenses force light rays to follow different paths through the indicatrixWEN-S polarizerWhat do we see??

Biaxial interference figuresThere are lots of types of biaxial figures well concentrate on only two

2. Bxa figure (acute bisectrix) - obtained when you are looking straight down between the two O.A.s. Hard to find, but look for a grain with intermediate d.

Biaxial interference figuresUse this figure to get sign and 2V:

Quick review:Indicatrix gives us a way to relate optical phenomena to crystallographic orientation, and to explain differences between grains of the same mineral in thin sectionIsotropic? Uniaxial? Biaxial? Sign? 2V?All of these help us to uniquely identify unknown minerals.

Mafic Igneous MineralsOlivine, Pyroxene, Amphiboles, Micas

So farWhat are the most important mineral (groups) that we have viewed so farQuartz (not a group but hey its everywhere)FeldsparPlagioclaseAlkali Feldspar

3 of the 6 most important minerals you will ever see

What are the other 3 Pyroxene

Amphiboles

Micas

Olivine, we had to stick it somewhere even though it is not as common as the ones above

OlivineLets get it out of the wayNesosilicateStronger bonds close packing of ions

What does that meanHigher index of refractionHigher hardness

Olivine It is actually a group of minerals Lumped together to be called Olivine End membersFayalite (Iron Silicate) Generally darker because it has ironHeavier, higher index of refractionForsterite (Magnesium Silicate)

Sadly its really tough to tell them apartSo we just lump them as Olivine

MicasPhyllosilicatesMost of these are flat and platy Lots of smooth and flat ones, also powders

Micas are a group of minerals as well containing 30 minerals You need to know all 30

Well there are 2- 3 big ones

Muscovite and BiotiteThin platy minerals that we have seen beforeBiotite is generally brown to blackMuscovite is white, silver, yellow, green

Not really going to say to much more

However glauconite is one of the important ones. Homework, go home and find out why I think it is importantI am serious

Amphiboles Chain silicates (single or double)Inosilicates Dark minerals in hand sampleOblique cleavage 120Generally have strong pleochroism HornblendeGlaucophaneWhat did these look like in PPL?

Amphibolesconstituent of igneous rocksoften making up the dark colored fraction of minerals in an igneous rock (sounds familiar) Hornblende is one common varietyYou don't generally find amphiboles and pyroxenes togetherThe presence of amphiboles indicates high pressure and the presence of fluorine and gaseous water (hence the hydroxyls)High pressure conditions suitable for the formation of amphiboles occur at great depth or under a tectonic load.

PyroxenesChain silicatesPyroxene means fire and stranger Because the greeks wanted to pick cool words for rocks to get undergrads interested in geology

(actually because they form in volcanic glass and they were thought to be impurities)

Pyroxene (ortho and Clino)First off tell them apart in hand sample from amphibole by their 90 Cleavage

Generally form in high temperate magmas with a lack of water.If there is water amphiboles would most likely form

Difference between clino and ortho comes from which crystal system they form underMore on that later in the year

Pyroxene (ortho/clino,)SiO6Pyroxenes are an important constituent in igneous rocksDark specks or are the reason for an overall dark color of a rockMost often confused with amphiboles which are similar in color and occurrence Distinguished by their cleavage angles. A mnemonic we grad students use goes like this: the "x" in pyroxene indicates cross-wise (square) cleavage. Pyroxenes are readily altered to other minerals such as calcite or limonite Monoclinic and Orthorombic

PyroxeneAugiteWollastoniteDiopsideEnstatiteHyperstheneThis contains both orthoAnd clino

Microscope stuff

Parallel and inclined extinctionInclined--mineral is dark when the crystal face of cleavage face forms an angle with the crosshairs of the microscope. The extinction angle is a diagnostic property of minerals. Hornblend is an example. All biaxial minerals excluding orthorhombic minerals have inclined extinction.

Parallel--mineral is dark when the crystal face or cleavage face is parallel to the crosshairs of microscope. An example is biotite. All uniaxial minerals have parallel extinction, but so do orthorhombic biaxial minerals (olivine, orth-pyroxenes).

OlivineModerately high relief Clear, occasionally very light yellowish or greenish No cleavage Commonly rimmed with greenish alteration products (A) Internal fracturing of grains common (B) Never occurs with quartz

Orthopyroxene All have low birefringence (first order red maximum),

parallel extinction,87 degree cleavage. Pale green, pale red, or pale purple pleochroism occurs in some grains.

Distinguished from clinopyroxene by low order interference colors and parallel extinction

Notice the extinction

Clinopyroxenegenerally difficult to distinguish between individuals in this group optically.All are moderate relief up to second order birefringence colors, 87 degree cleavage

and inclined extinction

AmphibolesCleave angleGreen brown pleo

muscoviteBirds eye extinctiongives the mineral a pebbly appearance as it passes into extinction. This is caused when the grinding tools used to create petrographic slides of precise widths alter the alignment of the previously perfect basal cleavage planes which split micas up into its characteristic thin sheets. The resulting, slightly roughened surface alters the extinction angle of various parts of the crystal lattice, leading to this type of extinction

high birefringenceparallel extinctionand excellent basal cleavage

Biotitestrong pleochroism in brown, reddish brown, and green hornblende has similar pleochroic colors and can be confused with biotite, hornblende has inclined extinction, not parallel extinction. Little black dots are radiation damage

Optical Mineralogy in a NutshellUse of the petrographic microscope in three easy lessonsPart III Jane Selverstone, University of New Mexico, 2003

JENIS PENGAMATANORTOSKOPISKONOSKOPISSinar-sinar yang datangnya sejajarSinar-sinar yang datangnya kerucut (lensa kondensor)PPL (nikol sejajar)XPL (nikol bersilang)Warna, pleokroisme, habit (bentuk), indek bias,belahan, relief, ukuranBias rangkap (BF), orientasi, pemadaman,sumbu optik, tanda optik, kembaran

IDENTIFIKASI MINERALOPAQTEMBUS CAHAYA(Transparan)ISOTROPANISOTROPTak terjadi perubahan warnaTerjadi perubahan warnaTak ada bias rangkap (BF)Terdapat bias rangkap (BF)Contoh: Mineral bijih, gelasContoh: RFMMikroskop PolarisasiMengacu pada indek warna

MINERAL PEMBENTUK BATUANMAFIKFELSIKRelief tinggiBerwarnaBF kuatRelief rendahTak berwarna/ transparanBF lemahMineral SilikatMineral Non-SilikatOksida (hematit, magnetit, rutil) Sulfida (pirit, spalerit, galena, kalkopirit) Phospat (apatit) Sulfat (anhidrit, gipsum) Karbonat (kalsit, aragonit, dolomit)(Seri Bowen, 1928)

A few new properties, and then some reviewCleavage number and orientation of cleavage planes

Twinning type of twinning, orientation

Extinction angle parallel or inclined? Angle?

Habit characteristic form of mineral

CleavageMost easily observed in PPL (upper polarizer out), but visible in XN as well No cleavages:quartz, olivine 1 good cleavage:micas 2 good cleavages:pyroxenes, amphiboles

Cleavage

Cleavagerandom fractures, no cleavage:olivine

Twinning Presence and style of twinning can be diagnosticTwins are usually most obvious in XN (upper polarizer in)

Twinning - some examplesClinopyroxene (augite)Plagioclase

Extinction angleExtinction behavior is a function of the relationship between indicatrix orientation and crystallographic orientation

Extinction angle parallel extinction All uniaxial minerals show parallel extinction Orthorhombic minerals show parallel extinction(this is because xtl axes and indicatrix axes coincide)PPLorthopyroxene

Extinction angle - inclined extinctionMonoclinic and triclinic minerals: indicatrix axes do not coincide with crystallographic axesThese minerals have inclined extinction (and extinction angle helps to identify them)clinopyroxene

Habit or formblockyacicularbladedprismaticanhedral/irregularelongateroundedfibroustabulareuhedral

Habit or formblockyacicularbladedprismaticanhedral/irregularelongateroundedfibroustabulareuhedral

Review techniques for identifying unknown mineralsStart in PPL: Color/pleochroism Relief Cleavages HabitThen go to XN: Birefringence Twinning Extinction angle Uniaxial or biaxial? 2V if biaxial Positive or negative?

Go to Nesse or similar book Chemical formula Symmetry Uni or biaxial, (+) or (-) RIs: lengths of indicatrix axes Birefringence 2V if biaxialDiagrams: Crystallographic axes Indicatrix axes Optic axes Cleavages Extinction angles

Another exampleThen read text re color, pleochroism, habit, cleavage, twinning, distinguishing features, occurrence make sure properties match your observations. If not, check another mineralCrystallographic axes: a, b, cIndicatrix axes: X, Y, Z or e, w

On to real rocksgood luck and have fun!

Mineral optik2 SKS teoriby:hill. gendoet hartonoSemester 3, 2009-2010Selasa, jam 09.50 10.40 jam 10.40 11.35

Thin sectionThin rectangular slice of rock that light can pass through.One side is polished smooth and thenstuck to a glass slide with epoxy resinThe other side is ground to 0.03 mm thickness, and then polished smooth.May be covered with a thin glass cover slip0.03 mm

Petrographic MicroscopeOcular LensObjective LensStageSubstage AssemblyIncluding lower polarizerLight and blue filterUpper Polarizer Focus

Identifikasi MineralOpaqTransparanWarnaBentukBelahanIndek RefraksiAnisotropisIsotropisBF/ BiasrangkapBiaxialUniaxial

Opaque MineralSulphides and oxidesPPL does not pass throughMinerals looks black in PPL regardless of orientation of mineral or polarizersMineral cannot be identified in transmitted light; needs reflected lightOpaque mineral in graniteRotated 45o in PPL

Transparent mineralPPL passes through the 30m thickness of the thin sectionThe electromagnetic light waves interact with the electrons in the minerals and slow downThe higher the density of electrons the slower the light wave travels

CPX in gabbroPPL

MINERAL PEMBENTUK BATUAN

SILICATES CONTAIN SILICON - OXYGEN MOLECULE (SiO)

NON-SILICATES (NO SiO)

NON-SILICATE MINERALSMake up 5% of Earths continental crustNative metals: gold, silver, copperCarbonates: calcite (used in cement)Oxides: hematite (iron ores)Sulfides: galena (lead ores)Sulfates: gypsum (used in plaster)

SILICATE MINERALSQUARTZ (SiO2)FELDSPARS (PLAGIOCLASE - (Na,Ca)(Si,Al)4O8 ) )MICAS (MUSCOVITE -KAl2(AlSi3O10)(F, OH)2, BIOTITE - K (Fe, Mg)3 AlSi3 O10 (F, OH)2 )AMPHIBOLES (Hornblende -Ca2(Fe,Mg)5Si8O22(OH2) ) PYROXENES (Augite {Mg,Fe}SiO3)OLIVINE - (Mg, Fe)2SiO4,

FELSIC SILICATE MINERALS FELSIC SILICATES HIGH % SiOQUARTZ (100% SiO2)FELDSPARSMUSCOVITE MICA (KAl2(AlSi3O10)(F, OH)2

MAFIC SILICATE MINERALSMAFIC SILICATES - LESS SiOBIOTITE MICAAMPHIBOLEPYROXENE

ULTRAMAFIC SILICATESULTRA MAFIC SILICATES - VERY LOW % SiOVERY RARE AT SURFACEOLIVINE

OlivineModerately high relief Clear, occasionally very light yellowish or greenish No cleavage Commonly rimmed with greenish alteration products (A) Internal fracturing of grains common (B) Never occurs with quartz

Fracture

MorfologiKomposisiCiri-ciriAsal-usulUmumnya membentuk fenokris di dalambatuan beku, prismatik, belahan rectangulartidak jelas, pada alterasi garis retakan melengkung. End member Fosterit (Mg) dan Fayalit (Fe). BF tinggi, tanpa belahan, rekahan melengkungterisi oleh produk alterasi.Mineral mafik dan ultramafik batuan beku,Penyusun utama matel Bumi.

Magnesium/ MgBesi/ Fe

Orthopyroxene All have low birefringence(first order red maximum),

parallel extinction,87 degree cleavage. Pale green, pale red, or pale purple pleochroism occurs in some grains.

Distinguished from clinopyroxene by low order interference colors and parallel extinction

Notice the extinction

Clinopyroxenegenerally difficult to distinguish between individuals in this group optically.All are moderate relief up to second order birefringence colors, 87 degree cleavage

and inclined extinction

MorfologiKomposisiCiri-ciriAsal-usulUmumnya membentuk kristal prismatikeuhedral. Mg/(Mg + Fe); Enstatit (100-88 mol %); bronzit (88-70); hipersten (70-50); fero-hipersten (50-30); eulit (30-12); ferosilit(12-0).Low BF Bronzit dan hipersten dijumpai dalam gabrotholeiit, diabas dan andesit kapur-alkali; ortopiroksin dalam batuan beku.

MorfologiKomposisiCiri-ciriAsal-usulKristal jarang berbentuk euhedral karenakristalisasi akhir antara kristal bentukan-awal; tumbuh sebagai reaksi rim disekitarortopiroksin.Klinopiroksin miskin Ca yang mengandung 10 mol % komponen wolastonit.Pigeonit lebih bersih dibanding augit.Umumnya piroksin miskin Ca dalam batuan subalkalin yang mempunyai Mg/(Mg+Fe) < 0,7.

MorfologiKomposisiCiri-ciriAsal-usulPenyusun utama batuan beku alkalin mafik dan subalkalin. Dalam batuan alkalin mengandung sejumlah Na atau Ti. Dalam batuan subalkalin berasosiasi dengan ortopiroksin atau pigeonit.Umumnya berbentuk prisma dalam batuan beku alkalin mafik dan andesit augit, tetapi di dalam batuan tholeiit cenderung anhedral.Komplit solid solution antara diopsit dan hedenbergit. Komposisi menengah dalam batuan tholeiit, sedikit Ca.Warna lebih cerah dibanding pigeonit dan sedikit terubah.

MorfologiKomposisiCiri-ciriAsal-usulKristalin prismatik panjang tetapi mungkin juga membentuk rim pada kristal augit. Solid solution dari augit ke aegirin dengan perubahan warna cerah ke hijau denganpeningkatan substitusi NaFe. Kristal umumnyazona dari augit di inti ke arah luar aegirin-augitke aegirin pada rim. Dibedakan oleh warna hijau rumput transparancerah; hijau amfibol sedikit transparan. Belahanmenyudut, pemadaman menyudut kecil.Terjadi pada batuan beku kaya Na. Mungkinberasosiasi dengan nefelin dan sodalit tetapijuga terjadi dengan kuarsa pada syenit alkalidan granit.

MorfologiKomposisiCiri-ciriAsal-usulMeniang hingga berserabut. Solid solution kearah diopsit, dalam eklogitlarutan ini luas, membentuk piroksin ompasit.BF rendah, punya belahan tapi berbeda denganpiroksin lain, pemadaman paralel.Stabil pada tekanan tinggi, terbatas hingga padabatuan metamorf skis glaukopan, eklogit.

AmphibolesCleave angleGreen brown pleo

MorfologiKomposisiCiri-ciriAsal-usulBerbentuk agregat dan berbutir prismatik di dalam batuan metamorf. Hadir sebagai fenokris, prisma bersisi 6 dalam batuan beku, cenderung memanjang dalam batuan beku asam.Antara tremolit-aktinolit dan pargasit-ferohastingsit.Umumnya tidak mudah dibedakan secara optik dari aktinolit. BF kuat.Salah satu RFM. Mineral feromagnesian dalam batuan beku kapur alkali. Mineral utama dalam batuan beku mafik yang termetamorkan.

Biotitestrong pleochroism in brown, reddish brown, and green hornblende has similar pleochroic colors and can be confused with biotite, hornblende has inclined extinction, not parallel extinction. Little black dots are radiation damage

MorfologiKomposisiCiri-ciriAsal-usulBerbentuk kristal tabular dalam batuan granit, dalam batuan gabro mengkristal terakhir berbentuk anhedral. Sangat luas, substitusi Mg Fe, Al Si. Kandungan Ti berwarna merah tua, kandungan Fe berwarna hijau.Pleokroik, belahan 1, pemadaman paralel. BF kuat.Salah satu RFM. Mineral feromagnesian dalam batuan beku granit. Mineral utama dalam batuan beku menengah seperti granodiorit, diorit, monzonit. Biotit dengan magnesium tinggi terjadi dalam kimberlit.

Plagioklas-XPL

Plagioklas-XPL

MorfologiKomposisiCiri-ciriAsal-usulBerbentuk prismatik tabular di dalam batuan beku. Hadir sebagai fenokris, cenderung membentuk lath tabular dalam batuan beku tetapi unhedral.Anotit-bitownit-labradorit-andesin-oligoklas-albit.Relief rendah, mempunyai banyak kembaran, albit, carlsbad, carlsbad-albit, periklin. Salah satu RFM. Umum dijumpai di seluruh kerak Bumi.

muscoviteBirds eye extinctiongives the mineral a pebbly appearance as it passes into extinction. This is caused when the grinding tools used to create petrographic slides of precise widths alter the alignment of the previously perfect basal cleavage planes which split micas up into its characteristic thin sheets. The resulting, slightly roughened surface alters the extinction angle of various parts of the crystal lattice, leading to this type of extinction

high birefringenceparallel extinctionand excellent basal cleavage

MorfologiKomposisiCiri-ciriAsal-usulBerbentuk kristal tabular paralel. Didalam batuan pegmatit muskovit berbentuk prisma sisi 6.Substitusi Na K menghasilkan paragonit, Mg atau Fe Al. Beberapa muscovit mengandung proporsi silika tinggi.Pemadaman paralel, pemadaman mata burung. BF kuat.Umum di dalam batuan skis pelitik yang terbentuk pada suhu rendah hingga menengah pada metamorfisme regional. Umum berasosiasi pada batuan pegmatit dan granit alumina.

Kuarsa-XPL

MorfologiKomposisiCiri-ciriAsal-usulJarang berbentuk euhedral kecuali di dalam vein. Polymorf alpha suhu rendah dan beta suhu tinggi. Berbentuk prisma pada kuarsa suhu rendah.Relief rendah, warna interferensi kuning pucat hingga kehijauan, pemadaman undulatori.Umum pada kerak benua. Komponen utama pada granit, batuan sedimen dan metamorf. Umum dijumpai atau terbentuk dalam vein.

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