Introduction to Petrography

Week #2Assistants : Feisal Dirgantara

… what we’ve learned from last week

How to learn petrology

•Outcrop

•Hand sample

•Thin section

•Chemistry

•Experimental Studies

Importance of petrography

• Petrogenesa

• Mineral composition and abundance

• What have altered after lithification

• Environmental of Deposition

• Type of deposition

• Post lithification structure, e.g stylolite, bioturbation, karstification

Light as wave-particle duality• Light as wave• Radiated energy which vibrates

at certain angle to the direction of motion

• Important characteristics :

• Amplitude

• Frequency

• Wave length

C = f.λ

• Light as particle

– When a photon is created, the light particle comes in and hits the electron so that it moves to the next energy cloud

– Due to instability of energy, the electron will bounce back to originial energy state and emits photon away

Oxygen (8O)

:: Light as wave-approach is the basis for petrography analysis

Snell’s Law

Θ2 : θ1 = C2 : C1 = λ2 : λ1

C = f.λ

θ1

θ2

air

Qz

Light’s polarization

• Normally, a light vibrates in circular polarization.

• A polarizer will adjust light wave to move in a specific polarization without changing its characteristic (wavelength, amplitude, speed, frequency).

Petrography microscope

Glossary in petrography• anisotropic mineral: A mineral with more than one principal

refractive index.

• birefringence: The mathematical difference between the largest and smallest refractive index for an anisotropic mineral.

• biaxial mineral: A mineral with three principal refractive indices and two optic axes. Its indicatrix is a triaxial ellipsoid.

• dispersion: Change of any optical property with wavelength.

• indicatrix: The three-dimensional surface describing the variation in refractive index with relationship to vibration direction of incident light.

• optical orientation: The relationship between a mineral's crystallographic axes and optical indicatrix.

• pleochroism: The property of exhibiting different colors as a function of the vibration direction.

• uniaxial mineral: A mineral with two principal refractive indices and one optic axis. Its indicatrix is a prolate or oblate ellipsoid.

• optical class: One of five possible classes (different indicatrices) to which a mineral can belong: isotropic, uniaxial +/-, or biaxial +/-.

• isotropic mineral: A mineral with the same refractive index regardless of vibration direction. Its indicatrix is a sphere.

Igneous Petrography

Week #2Assistants : Sony Adam, Ragil Yuni

1) Light passes through the lower polarizer

west (left)

east (right)

Plane polarized light“PPL”

Unpolarized light

Only the component of light vibrating in E-W direction can pass through lower polarizer – light intensity

decreases

PPL

XPL

west (left)

east (right)XPL

(crossed nicols or crossed polars)

south (front)

north (back)

Black!“extinct”

2) Insert the upper polarizer

Now what happens?What reaches your eye?

Why would anyone design a microscope that prevents light from reaching your eye?

3) Now insert a thin section of a rock

west (left)

east (right)

Light vibrating E-W

Light vibrating in many planes and

with many wavelengths

Unpolarized light

Light and colors reach eye!

XPL

PhotomicrographConclusion has to be that minerals somehow reorient the planes in

which light is vibrating; some light passes through the upper polarizer

PPL XPL

What are you looking for inPPL XPL• Color• Cleavage• Habit

• Grain boundaries• Twinning• Birefringence

Color• Color is observed only in PPL• Not an inherent property - changes with light type/intensity• Results from selective absorption of certain l of light

plag

hbl

-Plagioclase is colorless-Hornblende is olive greens

Cleavage• No cleavages: quartz, olivine• 1 good cleavage: micas• 2 good cleavages: pyroxenes, amphiboles

Cleavage

2 cleavages intersectingat ~90° pyroxene

60°

120°

2 cleavages intersectingat 60°/120°: amphibole

prismatic

anhedral/irregular

elongate

fibrous

tabular

euhedral

Habits

prismatic

anhedral/irregular

elongate

fibrous

tabular

euhedral

Habits

Birefringence, XPL Color Spectrum

Twinning

• Not only in hand samples

• Under the microscope • Parts will be extinct

while the other will show a true XPL color

• Very common in Plagioclase Feldspar

Degree of Crystallization

Holokristalin

Holocrystalline - composed wholly of crystalsHypocrystalline - contains both glass and crystalsHolohayline - consists entirely of glass

Granular TexturePanidiomorphic-granular (automorphic-granular) - the chief minerals are euhedral

Hypidiomorphic-granular (hypautomorphic-granular or granitic) - some constituents are euhedral, some subhedra, and the rest anhedral

Allotriomorphic-granular (xenomorphic-granular or aplitic or sugary or saccaharoidal ) – almost all of the constituents are anhedral

Porfiro-aphanitic Phaneritic

Quartz

Plagioclase & K-Feldspar

Biotite

Muscovite

Hornblende

Pyroxene (CPX & OPX)

Olivine

MineralPPL XPL

Warna Belahan Habit Twinning Birefringence

QZ Colorless -AnhedraIrregular

-1st

Abu - Putih

PLAG Colorless - Tabular Ya 1st

KSPARColorless

Abu- Tabular Ya 1st - Abu

BIOCoklatHijau

1 Tabular -Up to 2nd

Red

MUS Colorless 1 Tabular -Up to 2nd

Red

HRBHijauCoklat

2 (60°)Any

Anhedra-

Up to mid2nd

OPX Colorless 2 (90°)Any

Anhedra-

Up to 1st

Yellow

CPX Colorless 2 (90°)Any

Anhedra-

Up to high2nd

OLV Colorless - Tabular -Up to high

3rd

G Colorless - Anhedra - Black

OPQ Black - Anhedra - Black

Komposisi Mineral:• 60% Olivin. PPL: Tidak berwarna, Belahan poor, Habit: euhedral. XPL: No Twinning, Interferensi orde 2 sampai 3.

25% Plagioklas menjadi massa dasar.

15% Mineral Opaque. PPL: Warna hitam, habit: subhedral. XPL: Tak tembus/Orde 1, hadir setempat-setempat dalam sayatan

Tekstur:• Teksturnya adalah holokristalin, karena sebagian besar kristal• Komponen kristalnya porfiritik pada massa dasar yang afanitik• Fenokrisnya olivin yang euhedra sampai subhedra, dan beberapa plagioklas yang anhedra• Tekstur granularitasnya panidiomorfik granular.

Sedimentary Petrography

Week #2Assistants : Paula Ascariyani E Agung Dwi A.

Siliciclastics

Petrografi Batuan Sedimen

Jenis dari Batuan sedimen, berdasarkan mekanisme sedimentasinya

•Dentrital

•Nondentrital / Authigenic

Komposisi batuan sedimen, dilihat dari batuan induknya• Menunjukkan bagian besar yang sama dari

sedimen dentrital.

• Karena Diagenesis , maka batuan memiliki bentuk yang benar2 berbeda dari batuan induknya.

• Terlihat komposisi batuan berupa mineral yang stabil seperti Quartz, Mica, dan Feldspar.

Akibat Transportasi dan Deposisi

• perubahan fisik dari batuan, perubahan dari bentuk, ukuran, dan derajat kebolaan. Karena proses sortasi dan abrasi.

• perubahan fisik dari batuan, perubahan dari bentuk, ukuran, dan derajat kebolaan. Karena proses sortasi dan abrasi.

Akibat Transportasi dan Deposisi

• Partikel ukuran paling besar dan densitas besar, akan terdeposisi pertama kali.

• Perubahan secara fisik ini akan terlihat dan mencirikan tekstur dari batuan sedimen.

UKURAN BUTIR

UKURAN BUTIRUkuran butir akan menunjukkan energi pengendapan

Ukuran kecil = energi kecilUkuran besar = energi besar

–Ketika aliran sedikit memelan, hanya kan mengendapkan partikel yg terbesar dan mengendapkan sedimen dengan sortasi yang baik.

–Ketika aliran semakin pelan, akan mengendapkan partikel sedimen dg ukuran yg bervariasi (semua ukuran, diatas kompetensi yg baru), dan akan mengendapkan sedimen dg sortasi buruk.

SORTASI DAN BENTUK BUTIR

• 1. SORTASI

• 2. BENTUK BUTIR

HUBUNGAN ANTAR BUTIR

Line of Traverse(using microscope)

Cement

Matrix(clays, etc.)

Tangential Contact

Sutured Contact

Long Contact

Concavo-ConvexContact

HUBUNGAN ANTAR BUTIR

(modified from Blatt, 1982)

HUBUNGAN ANTAR BUTIR

TIPE POROSITAS

TIPE POROSITAS

KOMPOSISI

KLASIFIKASI

After Pettijohn et al. (1987)

KOMPONEN SILISIKLASTIK

1. PASIR SILISIKLASTIK

• Kuarsa, Feldspar, dll

2. MUD

• Mineral Lempung

CONTOH SAYATAN

Feldspar Plagioklas

K-Fldspar

Karbonat

FELDSPATHIC ARENITE

HANDSPECIMEN FELDSPATHIC ARENITE

CONTOH SAYATAN

QUARTZ ARENITE

Long contact

Sutured contact

Point contact

Convex -concav

HANDSPECIMEN QUARTZ ARENITE

LITHIC ARENITE

Lithic

Semen

Carbonates

Definisi

• Syarat Kondisi : (dominan dari proses biogenik) -> air laut• Hangat -> 19o - 25o C (zona photic dan iklim

tropis)

• Tenang arusnya

• Suplai sedimen darat minimum

Komponen Utama Batuan Karbonat

KLASIFIKASI

Folk Klasifikasi

Dunham Klasifikasi

Embry Klovan Klasifikasi

KEY : TEKSTUR PENGENDAPAN (ALLO ATAU AUTO)

Packestone

Grainstone

Floatstone

Rudstone

Matriks Supp

Grain Supp

Porositas

• Porositas intergranular, yaitu ruang pori yang terbentuk antar butiran partikel atau fragmen material klastik akibat batuan yang memiliki kemas lepas (looses packing), terkompaksi atau tersementasi.

• Porositas intragranular atau interkristalin, terbentuk akibat adanya shrinking (lenyapnya butiran akibat reaksi kimia) atau kontraksi butiran.

• Porositas rekahan, diakibatkan oleh adanya proses mekanik atau proses kimiawi secara parsial terhadap batuan yang masiv pada awalnya, seperti batu gamping. Porositas jenis ini merupakan porositas sekunder.

• Porositas vugular, adalah porositas yang dibentuk oleh organisme dan bersamaan dengan terjadinya proses/ reaksi kimia pada tahapan selanjutnya. Porositas ini merupakan jenis porositas primer dan sekunder.

Metamorphic Petrography

Week #2Assistants : Yuni Indrawati Fitrul Islam

• Klasifikasi batuan metamorf

• Tipe Metamorfisme :

Primary rocktype

Fineless than 1.0

mm

Medium1.0-5.0 mm 

CoarseGreater than 5.0 mm

Diagnostic Minerals

PELITES    Shales, mudstones and clays rich rocks. Aluminous.

Slate or phyllite Schist Gneiss, Migmatite

Quartz, White mica, biotite, chlorite,  garnet, staurolite,  andalusite/kyanite/sillimanite, cordierite,  corundum, chloritoid.

PSAMMITES  Sandstones, greywackes.  quartz-feldspar rich minor mafics.

Quartzite Quartzite QuartziteQuartz, alkali feldspar, white mica,  biotite, rare amphibole, chlorite.

CALCAREOUS  Pure limestone's and dolomites. Ca, Si and Mg.   

Marble Marble Marble Calcite, minor quartz and micas.

CALC-SILICATES  Shaly and quartz rich  dolomites and limestones. Marls. Ca and Si.

Calc-slate Calc-schist Calc-gneissCalcite, quartz, epidote, Ca-plagioclase,  Grossular garnet, Diopside, Tremolite,  Talc, Sphene, Forsterite, Actinolite.

QUARTZO-FELDSPATHIC  Granitic and rhyolitic rocks.  Quartz, feldspar, amphiboles and mica.

Halle-flintaAcid or granitic gneiss

Acid or granitic gneissQuartz, White mica, Biotite,  Plagioclase, Alkali feldspar, Sphene.

MAFIC  Gabbros and basaltic rocks  Fe and Mg rich.

Greenstone  Greenschist   

AmphiboliteBasic, Hornblende or pyroxene gneiss

Epidote, Sphene, Calcite, Chlorite,  Amphibole, Pyroxene, Plagioclase,  Garnet, Serpentine, Talc.

ULTRAMAFIC peridotites, dunites pyroxenites, lacking feldspar. Very rich in Fe and Mg.

 Serpentinite  Talc-schist  Soapstone

Ultrabasic gneissSerpentine, Talc, Phlogopite,  Forsterite, Anthophyllite, Brucite,  Enstatite, Magnesite-dolomite, Cordierite.

A. Granoblastik, B. Granoblastik (butir tak teratur), C. Schistose dengan porfiroblast, D. Schistose dengan granoblastik lentikuler, E. Filitik, F. Gneissose, G. Milonitik, H. filonitik, I. Granoblastik dalam milonit.

Bentuk Kristal Keterangan

(Euhedral) Staurolit, silimanit, kianit, rutil, klorit, ilmenit, turmalin, pirit, lawsonit, andalusit, garnet, sfen, epidot, zoisit, magnetit, spinel, ankerit, idokras

(Subhedral) Mika & klorit (memipih), amfibol & piroksen (prismatik), wolastonit, dolomit & apatit

(Anhedral) Kuarsa, felsfar, kalsit, aragonit, olivin, kordierit, scapolit, humites

Sketsa bentuk butir (kristal/mineral) a. euhedral, b. subhedral, c. anhedral

Tabel determinasi batuan metamorf

GARNET-AMPHIBOLITE

Bertekstur heteroblastik

terdiri dari mineral hornblende, garnet, mineral opak

terlihat struktur masif yang dominan oleh mineral garnet dan hornblenda

• Hornblende• 30 %

• Ukuran 0,2 – 1 mm

• Mineral nematoblastik

• Membentuk sekistose

• Berbentuk prismatik subhedral-anhedral

• Garnet• 45%• Ukuran 0,6 – 1,5• Phorphyroblastic• Membentuk sekistose• Berbentuk anhedral