gd 4 mineral-batuan.pdf

8/19/2019 GD 4 mineral-batuan.pdf

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Geologi Dasar(MGD 301)

Materi 4

Program Studi Teknik Perminyakan

Fakultas Teknologi Mineral dan EnergiUniversitas Trisakti2009


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Quiz - 15 menit! 1. Tektonik lempeng merupakan proses yang

menjelaskan fenomena - fenomena alam dibumi,

sebutkan dan jelaskan 3 bentuk interaksi antarlempeng bumi.

! 2. Sebutkan bagian bagian bumi berdasarkankomposisinya

! 3. Sebutkan slogan uniformatarianisme

! 4. Sebutkan min. 3 hukum steno

! 5. Berapa panjang jari - jari bumi?

2


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Materi 4- PENGERTIAN GEOLOGI

- BUMI SEBAGAI PLANET- LITHOSFERA - MINERAL- BATUAN : BT, BEKU

BT SEDIMENBT, METAMORP


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MINERAL

! Dalam pengertian geologi mineral adalah zat atau benda yangterbentuk oleh proses alam, biasanya bersifat padat, tersusun dari

komposisi kimiawi tertentu serta mempunyai sifat fisik yang

tertentu pula

! Mineral terbentuk dari atom-atom serta molekul-molekul dari

berbagai unsur kimia, dimana atom-atom tersebut tersusun dalam

suatu pola yang teratur

! Keteraturan dari rangkaian atom ini menjadikan mineral

mempunyai sifat dalam yang teratur


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From: Plummer et al.

Mineral: A naturally occurring inorganic element or compound

having orderly internal structure and characteristic chemical

composition, crystal form, and physical properties.


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Groups or Families

Periods


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Unsur Mineral! Di alam ini terdapat sekitar 2000 jenis mineral yang telah diketahui.

Mineral-mineral tersebut ada yang tersusun oleh unsur tunggal,adapula yang terdapat sebagai persenyawaan.

! Yang terdiri dari unsur tunggal misalnya ;Au = aurum = emas

Ag = Argentum = perak Cu = Cuprum = tembagaC = Carbon = dalam bentuk allotropi

= Keadaan dimana Dua zat atau lebih mempunyai sifat kimiawi samatetapi berbeda dalam sifat fisiknya) berbentuk intan atau grafit


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Graphite & CalciteNatural Octahedral Diamond

3 mm

From: http://www.phy.mtu.edu/~jaszczak/diamond.html


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Mineral yang merupakan Senyawa

Kimia! CaCO3 = KALSIT

! CaSO4 2H2O = GYPSUM

! SiO2 = KWARSA! NaCl = HALIT

! KAlSi3O8 = FELSPAR ORTOKLAS

!

Fe3O4 = MAGNETIT! CuFeS2 = CHALCOPYRIT


10/74Halite Atomic Structure

Chemical Formula: NaCl

Note Cubic Symmetry and Closest Packing

Chemical compound: Two or more elements joined together by

a chemical bond. Most minerals are composed of at least two

elements.


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Rocks versus Minerals

Feldspar: NaAlSi3O8 - KAlSi3O8

Quartz: SiO2

Biotite: KMg3AlSi3O10(OH)2 -

KFe3AlSi3O10(OH)2

Granite rock type

Rock: an aggregate of one or more

minerals; in this case there are three

minerals present.


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Contoh Batuan Kerak Benua bagian bawah

Granulite

Gambar menunjukkan sayatan tipis batuan dalam miroskopis/petrografi dan

contoh ambilan tangan granulite (hand

specimen)


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Contoh Mineral Pembentuk Batuan

diantaranya memiliki nilai ekonomis untuk

komoditi karena unsur yang dikandungnya Analcime Andalusite Anhydrite

AntimonyAragonite Arsenopyrite Augite Barite Beryl

Bornite

Brazilianite Brookite Calcite CassiteriteChalcocite

Chalcopyrite Chrysoberyl

Corundum

Cryptomelane Cuprite Cyanotrichite

Diopside

Dioptase

Epidote Feldspar Ferberite

Danburite


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Perhiasan yang dipergunakan adalah preciousgems/jewelry yang berasal dari logam dan

mineral di bagian interior bumi dan mutiara daridasar samudra

Gems & Jewelry


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Sifat Fisik Mineral dan Batuan

!Unsur-unsur penyusunan bumi/

batuan terjadi dalam bentukmineral : secara langsung mineral

dapat dikenal dari sifat fisiknya antara lain :


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1. Bentuk Kristal (Crystal Form)Mineral dan Batuan

- Umumnya mineral mempunyai

bentuk kristal dan hanya sedikityang berbentuk amorf (antara lain

kalsedon dan opal, variasi mineralsilikat).


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1 - 5 mm

From: http://www.its.caltech.edu/~atomic/snowcry

Hexagonal Symmetry

Oddly, ice is less dense than liquid water,

hence it floats and lakes freeze from the

top down!


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BENTUK DASAR DARI KRISTAL :

! - ISOMETRIK - CONTOH : GALENA, HALITE &INTAN.

!

- TETRAGONAL - CONTOH : ZIRCON.! - HEKSAGONAL - CONTOH : KUARSA.

! - ORTHOROMBIK - CONTOH : TOPAS.

! - MONOKLINIK - CONTOH : GITHOKLAS

! - TRIKLINIK - CONTOH : PlAGIOKLAS

! DAN MASIH BANYAK VARIASI BENTUK KRISTALLAINNYA.


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Silicon Tetrahedron: SiO4 (net -4 charge)


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Olivine Structure: (Mg,Fe)2SiO

4


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Quartz Interfacial Angles

Perfectly

ProportionedCrystals

Misshapen

Crystals

Steno’s Law: Crystal face internal angles remain constant!


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Macroscopic Forms and Microscopic Blocks

Cubes

Rhombs

Macroscopic

Crystal Forms


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Crystal Forms: Quartz


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2. SISTIM BELAHAN (CLEAVAGE )

! Umumnya setiap mineral akan pecah menurut pola tertentu

sesuai sistim belahan mineral tersebut, sistim belahan tersebut

disebut 'cleavage'.

! Contoh : mineral mika mempunyai sistim belahan yang baik,yaitu ia akan pecah menurut bidang cleavege berlembar-lembar.

! Ada beberapa meneral mempunyai belahan dua arah ialah

kelompok mineral pyroxene; dengan sistim kedua belahan

membentuk sudut 90 °! meneral amphibol membentuk sudut 55 °

! Sistim belahan melengkung (conchoidal) seperti terdapat pada

meneral glass dan kalsedon.


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Planer Cleavage in Mica


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Weak Bonding Yields Planer Cleavage


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Amphibole Cleavage ~120/60°


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Rhombohedral Cleavage in Calcite


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Conchoidal Fracture in Glass


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Chrysotile Asbestos

Belongs to the Serpentine mineral family -

hydrated ferromagnesian silicate.


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3. Dera at Kekerasan Hardness

! Kekerasan • suatu ketahanan terhadap goresanoleh benda lain kekerasan ini relatif sifatnya.

! STANDARD KEKERASAN DARI MOHS


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The Physical Properties of Minerals (cont.)

! Fracture

! Specific Gravity

! Special Properties

! Other Properties

! Chemical Tests


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Physical properties of minerals

! Based on the principles discussed during thelast lecture and above, we now know thatminerals are composed of atoms, arranged in a

specific order, with a well defined chemicalcomposition. We might expect then that themicroscopic variations in bond environmentdiscussed above, will also be manifested inmacroscopic physical and chemicalproperties. This is indeed the case.


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Important Physical Properties I! Luster - This property describes the appearance of

reflected light from the mineral's surface. Nonmetallic

minerals are described using the following terms:

vitreous, pearly, silky, resinous, and earthy.


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Important Physical Properties II! Color - Although an obvious feature, it is often

unreliable to use to determine the type of mineral.

! Color arises due to electronic transitions, often of trace

constituents, in the visible range of the EM spectrum.For example, quartz is found in a variety of colors.

! Color of a mineral may be quite diagnostic for thetrace element and coordination number of its

bonding environment.


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http://www.nmnh.si.edu/minsci/hope


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Important Physical Properties III! Streak - The color of a mineral in its powdered

form; obtained by rubbing the mineral against anunglazed porcelain plate.

! Streak is usually less variable than color.

! Useful for distinguishing between minerals with

metallic luster.


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Density and Specific Gravity

! Density - Defined as the mass divided by thevolume and normally designated by the Greekletter, rho, !.

!

! =

mass/volume; SI units: kg/m3

or kg m-3

, butgeologists often use g/cm3 as the unit of choice.

! Specific Gravity - Ratio of the mass of a substanceto the mass of an equal volume of water. Note that

!water = 1 g cm

-3

. S.G. is unitless.! Examples - quartz (SiO2) has a S.G. of 2.65 while

galena (PbS) has a S.G. of 7.5 and gold (Au) has aS.G. of 19.3.

C l d


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Color and Density! Two broad categories are ferromagnesian and nonferromagnesian silicates , which

simply means iron and magnesian bearing or not. The presence or absence of Fe and Mgstrongly affects the external appearance (color) and density of the minerals.

! Ferromagnesian silicates - dark color, density range from 3.2 - 3.6 g/cc! Olivine - high T, low silica rocks; comprises over 50% of upper mantle! Pyroxenes - high T, low silica rocks

! Amphiboles - esp. hornblende; moderate T, higher silica rocks

! Mica - esp. biotite; moderate T, higher silica rocks

! Garnet - common metamorphic mineral

! Nonferromagnesian silicates - light color, density close to 2.7 g/cc! Mica - exp. muscovite; moderate T, higher silica rocks! Feldspars - plagioclase and orthoclase; most common mineral in crust; form over a

wide range of temperatures and melt compositions

! Quartz - low T, high silica rocks; extremely stable at surface, hence it tends to be amajor component in sedimentary rocks.

! Clay - esp. kaolinite; different types found in different soils


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From http://www.geo.wvu.edu/~lang/Geol284/Min8IgFels


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Zoning in Plagioclase Feldspar

Ca-rich core

Na-rich rim


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Note complex zoning pattern:

Ca content increases , then

decreases from core to rim.

Can interpret these chemical

data as indicating influx of

Ca-rich magma (basalt) into

a pre-existing magma chamber

prior to eruption!

From: Zellmer et al., J. Pet. 2003

Ca increases

Ca decreases


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Important Physical Properties IV! Crystal form or habit - The external

morphology of crystals generally reflect the

internal arrangement of their constituent atoms.

This can be obscured, however, if the mineral

crystallized in an environment that did not allow it

to grow without significant interaction with other

crystals (even of the same mineral).


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Chrysotile Asbestos

Belongs to the Serpentine mineral family -

hydrated ferromagnesian silicate.

E i Cl


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Expansive Clays


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Crystal Forms: Quartz


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Feldspar


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Intergrown cubic crystals of fluorite



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Perfectly

ProportionedCrystals

Misshapen

Crystals

Steno’s Law: Crystal face internal angles remain constant!



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Cubes

Rhombs

Macroscopic

Crystal Forms

Unit Cells and Crystal Structure


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Unit Cells and Crystal StructureCubic unit cell:

smallest repeatable unit


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Important Physical Properties V! Hardness - This is the resistance of the mineral

to abrasion or scratching. This property doesn'tvary greatly from sample to sample of the samemineral, and thus is highly diagnostic. It also is adirect reflection of the bonding type and internalatomic arrangement. A value is obtained by

comparing the mineral to a standard scaledevised by Moh , which is comprised of 10minerals ranging in hardness from talc (softest) todiamond (hardest).


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Graphite & CalciteNatural Octahedral Diamond

3 mm

From: http://www.phy.mtu.edu/~jaszczak/diamond.html


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From: http://www.molecules.org/elements.html#dia

Hardness: 10 Hardness: 1-2


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Fingernail Hardness (2.5) Scratches Gypsum (2)


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Important Physical Properties VI! Cleavage - Orientation and number of planes of

weakness within a mineral. Directly reflects the

orientation of weak bonds within the crystalstructure. This feature is also highly diagnostic.

! Fracture - This describes how a mineral breaks if

it is not along well defined planes. In minerals

with low symmetry and highly interconnected

atomic networks, irregular fracture is common.

Planer Cleavage in Mica


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g


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Weak Bonding Yields Planer Cleavage

Amphibole Cleavage ~120/60°


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Amphibole Cleavage ~120/60

Rhombohedral Cleavage in Calcite


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g



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S i l d Oth P ti


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Special and Other Properties! Striations - Commonly found on plagioclase

feldspar. Straight, parallel lines on one or more ofthe cleavage planes caused by mineral twinning.

! Magnetism - Property of a substance such that itwill spontaneous orient itself within a magneticfield. Magnetite (Fe3O4) has this property and it

can be used to distinguish it from other non-magnetite iron oxides, such as hematite (Fe2O3).

! Double Refraction - Seen in calcite crystals.Light is split or refracted into two componentsgiving rise to two distinct images.


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Plagioclasestriations


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Calcite Double Refraction

X ray diffraction: Laue


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X-ray diffraction: Lauephotographic method


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From: http://www.geology.wisc.edu/~g203/xray.


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From: http://www.geology.fau.edu/course_info/fall02/gly4200/X-R


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Formula:Ca10(Mg,Fe)2Al4Si9O34(OH)4System: TetragonalHardness: 61⁄2

http://www.mindat.org/min-4223.html

Modern Crystal Structure Determinations


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Modern Crystal Structure Determinations

! Get a compositional determination using the electron microprobe.! Determine space group from Precession and or Weissenberg photos.

! Measure x-ray intensities with automated diffractometer.

! Use Fourier analysis to derive electron density maps and locate

particular atoms in positions consistent with the space group.

! Calculate what the pattern should look like for your derived structure(both positions and intensities for all reflections).

! Compare calculated and observed intensities and calculate the percent

disagreement - the residual or error R.

! 20 years ago an R or 10% was good using film techniques.

! Now R should approach 4% for a convincingly good structure

determination.


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Terima kasih

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- Prodi Teknik Geologi FTKE Usakti

- Museum Geologi- Pusat Survei Geologi- Pusat Lingkungan Geologi- Pusat Vulkanologi & Mitigasi Bencana Geologi- Berbagai Situs Internet

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