ETROLO

U NA P

[TGS7404]

Dr. Hill. Gendoet Hartono

Semester 7, 2017-2018

2 SKS teori

GI BA

GI

T UAN

PENDAHULUAN 1X

Berisi tentang latarbelakang, bumi, batuan beku dan

batuan gunung api, dan kedudukan di bidang geologi

TATAAN TEKTONIK 2X

Berisi tentang tektonik global, regim tektonik, dan

peranannya dalam magmatisme dan volkanisme

GENERASI MAGMA 2X

Berisi tentang magmatisme, diagram fase

KLASIFIKASI 2X

Klasifikasi magma atau afinitas magma

Rock Forming Mineral 1X

Kimia Mineral Pembentuk Batuan 1X

Petrologi Batuan Intrusi Dangkal 2X

Petrologi Batuan Ekstrusi 2X

Alterasi Batuan Gunung Api 1X

SILICATE MINERAL CLASSIFICATION(BASED ON ARRANGEMENT OF SIO4 TETRAHEDRA)

The mineral olivine is a magnesium iron silicate with the formula (Mg2+,

Fe2+)2SiO4. Thus it is a type of nesosilicate or orthosilicate. It is a common

mineral in the Earth's subsurface but weathers quickly on the surface.

The ratio of magnesium and iron varies between the two endmembers of the

solid solution series: forsterite (Mg-endmember: Mg2SiO4) and fayalite (Fe-

endmember: Fe2SiO4). Compositions of olivine are commonly expressed as

molar percentages of forsterite (Fo) and fayalite (Fa) (e.g., Fo70Fa30). Forsterite

has an unusually high melting temperature at atmospheric pressure, almost

1,900 °C (3,450 °F), but the melting temperature of fayalite is much lower

(about 1,200 °C [2,190 °F]). The melting temperature varies smoothly between

the two endmembers, as do other properties. Olivine incorporates only minor

amounts of elements other than oxygen, silicon, magnesium and iron.

Manganese and nickel commonly are the additional elements present in

highest concentrations.

Olivine gives its name to the group of minerals with a related structure (the

olivine group) which includes tephroite (Mn2SiO4), monticellite (CaMgSiO4)

and kirschsteinite (CaFeSiO4).

Olivine in Gabbro

OLIVINE END-MEMBERS

• Forsterite Mg2SiO4

• Fayalite Fe2SiO4

•Tephroite Mn2SiO4

• Liebenbergite Ni2SiO4

•Co-olivine Co2SiO4

•Ca-olivine Ca2SiO4

•Monticellite CaMgSiO4

•Kirschsteinite CaFeSiO4

•Glaucochroite CaMnSiO4

OLIVINE OCCURRENCES

• Forsterite - Fayalite

Fo90 Olivine is major mineral of upper mantle

Minor phase in basalt and gabbro

Fayalite is secondary in silicic volcanics

• Monticellite accessory in mantle nudules

• Tephroite and glaucochroite

silicic volcanics and Mn skarns

• Liebenbergite secondary in Ni deposits

Fe Mg

Si

fayalite forsterite

enstatite ferrosilite

Pyroxene solid solution MgSiO3 – FeSiO3

Olivine solid solution Mg2SiO4 – Fe2SiO4

Fe Mg

forsteritefayalite

INOSILICATES (CHAIN)

• XY(Si2O6) in Pyroxenes, WX2Y5Si8O22(OH,F)2 in Amphiboles

• Single and double silicon tetrahedra chains respectively

• Typically monoclinic and orthorhombic symmetry

• Single chains (Pyroxenes) develop ~90° cleavage

• Double chains (Amphiboles) develop 120 ° cleavage

Amphibole StructurePyroxene Structure

Orthorhombic Pyroxenes (Orthopyroxenes - Opx)These consist of a range of compositions between Enstatite - MgSiO3 and Ferrosilite - FeSiO3

Monoclinic Pyroxenes (Clinopyroxenes - Cpx)The Diopside- Hedenbergite series - Diopside (CaMgSi2O6) - Ferrohedenbergite (CaFeSi2O6)

Augite - (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6 is closely related to the Diopside - Hedenbergite series with addition of Al and minor Na substitution

There is complete Mg-Fe solid solution between Diopside and (Ferro)Hedenbergite

There is also a complete Mg-Fe substitution and small amounts of Ca substitution into the Orthopyroxene solid solution series. Old name Hypersthene

Pigeonite is a high Temperature clinopyroxene

SOLID IMMISCIBILITY

Pigeonite is only found in hot volcanic and shallow intrusive igneous rocks, or as exsolution lamellae

Pigeonite crystallizes in the monoclinic system, as does Augite, and a miscibility gap exists between the two minerals.

Cpx

At lower temperatures, Pigeonite is unstable relative to Augite plus Orthopyroxene.

Pigeonite => Augite + Opx

Pigeonite (Ca,Mg,Fe)(Mg,Fe)Si2O6

Augite (Ca,Na)(Mg,Fe,Al)(Si,Al)2O6

Opx

COMMON PYROXENE SPECIES

Augite (Cpx)

Diopside (Cpx)

Enstatite (Opx)

COMMON TYPES OF AMPHIBOLES

COMMON PHYLLOSILICATES

Antigorite

ChrysotileKaolinite

Talc

Pyrophyllite

Muscovite

Lepidolite

BiotiteChlorite

Prehnite

Tectosilicates (Framework)

3-D framework of linked silicon tetrahedra

Variable physical properties and symmetries depending on linkage of framework groupings

SIO2 GROUP

Quartz SiO2

FELDSPAR GROUPMost abundant minerals, by mass or volume, in the crust

Compositionsfor Feldspars are commonly described in terms of mole percents of the end membercomponents (e.g. Or85Ab15, An54Ab39)

Microcline

Anorthite

XAl(Al,Si)3O8

Notice that Albite is an end member of both the Plagioclase and K-Spar (Alkali Feldspar) groups

Albite

ALKALI FELDSPARS

Perthite (albite exsolution in microcline)

Triclinic K-spar “Microcline”

Sanidine

Albite

At low temperatures solid solution (ss) is unstable, ss exsolves to Albite + Microcline. We say the two phases are immiscible