rocks

Question 1

What are the most common and important minerals?

Answer 1

Quarts, feldspar (plagioclase, alkali feldspar)
Micas (Ms, Bt, Chl)
Amphiboles
Pyroxenes
Calcite and dolomite
Garnet
Olivine

Question 2

Excluding the most common minerals, what important minerals are also found in igneous rocks?

Answer 2

zircon, apatite, titanite, rutile (accessories)

cordierite (mostly granites)

leucite, nepheline (alkali igneous; feldspathoids)

tremolite, actinolite, epidote, serpentine (alterations)

Question 3

Excluding the most common minerals, what important minerals are also found in metamorphic rocks rocks?

Answer 3

staurolite, andalucite, kyanite, sillimanite, cordierite,

epidote, glaucophane, rutile, titanite, diopsite, tremolite, actinolite, serpentine (+serpentinites), phlogopite (marbles)

Question 4

Excluding the most common minerals, what important minerals are also found in sedimentary rocks?

Answer 4

zircon, apatite, titanite, rutile, gypsum, anhydrite, halite, glaucophane, hematite, calcite

Question 5

What minerals characterise acid igneous rocks and what is the word used to describe the colour of these minerals?

Answer 5

Quartz and feldspar (leucocratic)

Question 6

What minerals characterise intermediate igneous rocks and what word is used to describe the colour of these minerals?

Answer 6

Plag = mafics (50:50)

Hornblende common but can be pyroxene (mesocratic)

Question 7

What minerals characterise basic igneous rocks and what word is used to classify these minerals?

Answer 7

Plag + Pyroxene (melanocratic)

Question 8

What minerals characterise ultrabasic igneous rocks?

Answer 8

Olivine + mafics (melanocratic) (ultrabasic often green HS due to abundant olivine)

Question 9

What are the main minerals to look out for in a hornfels?

Answer 9

Cordierite, Andalusite

Question 10

What index minerals characterize the Greenschist facies?

Answer 10

Garnet, Chlorite and Biotite

Question 11

What index minerals characterize the Amphibolite facies?

Answer 11

Staurolite, Kyanite, Sillimanite

Question 12

What minerals are indicative of a Blueschist facies rock?

Answer 12

Glaucophane and lawsonite

Question 13

What minerals are indicative of a Eclogite facies rock?

Answer 13

Garnet and omphacite

Question 14

What’s the field of view on x4 magnification?

Answer 14

4.4mm

Question 15

What’s the field of view on x10 magnification?

Answer 15

1.8mm

Question 16

What’s the field of view on x40 magnification

Answer 16

0.4mm

Question 17

What grain size is a medium grained igneous rock?

Answer 17

1mm-3mm

Question 18

What grain size is a coarse grained igneous rock?

Answer 18

3mm-3cm

Question 19

What grain size is a very coarse grained igneous rock?

Answer 19

>3cm

Question 20

What mineral? Cleavage: Two: perfect [001], good on [010] PPL: Colourless, No pleochroism, Low relief XP: First order δ (greys), commonly exhibits simple Carlsbad twins

Answer 20

Sanidine

Question 21

What are the optical properties of sanidine?

Answer 21

Cleavage: Two: perfect [001], good on [010] PPL: Colourless, No pleochroism, Low relief XP: First order δ (greys), commonly exhibits simple Carlsbad twins

Question 22

What is the difference between cpx and opx?

Answer 22

Cpx has inclined extinction while Opx has straight extinction Cpx max 2nd order birefringence while Opx max first order

Question 23

What is the difference between an amphibole and a px?

Answer 23

Amph has 2 intersecting at 124°/56° (in basal sections) and px has 2 at 90° (only seen in basal sections) Amph often has strong body colour that masks its 1st to low 3rd order birefringence.

Question 24

What is the distinguishing feature of titanite?

Answer 24

Lozenge shaped

Question 25

What is the distinguishing feature of zircon?

Answer 25

Forms pleochroic haloes in biotite

Question 26

Chiastolite is a type of what?

Answer 26

Andalusite

Question 27

What are the distinguishing features of Andalusite?

Answer 27

highly symmetrical parallelogram shaped basal sections chiastolite has black cross in basal section

Question 28

What are the distinguishing features of Kyanite?

Answer 28

Two well-developed ≠ 90° (but close to 90 so can be confused with pyroxene) Often bladed, elongate laths PPL: Characteristically pale blue, moderate-high relief XP: Inclined extinction, low 1st order δ

Question 29

In what rock is sanidine most likely to be found?

Answer 29

Sanidine is a high temperature, potassium-rich alkali feldspar, Typically forms tabular laths, Occurs in silicic lavas (rapidly cooled igneous rocks)

Question 30

What are the distinguishing features of olivine?

Answer 30

PPL: High relief, curved fractures, weathering (serpentine, iddingsite) XP: 2nd – 3rd order δ

Question 31

What are the distinguishing features of Sillimanite?

Answer 31

PPL: Fibrous masses or acicular, moderate-high relief, colourless to yellow brown

Question 32

What are the distinguishing features of Garnet?

Answer 32

PPL: High relief, colourless to pale pink XP: Isotropic (because cubic), often poikilitic

Question 33

What are the distinguishing features of cordierite?

Answer 33

PPL: Low to negative relief, usually colourless, often filled with many tiny inclusions XP: Low 1st order δ, weathers easily to mixture of clay minerals + muscovite called pinite – alters centre of crystal Common in LP/HT contact metamorphism of mudstones, LP equivalent to garnet, form large crystals (up to 0.5cm)

Question 34

What are the distinguishing features of staurolite?

Answer 34

PPL: Almost always has honey yellow colour, strong pleochroism XP: Low order δ colours masked by body colour

Question 35

What are the optical properties of lecite?

Answer 35

cleavage: none: very poor PPL Colour: colourless Pleochroism: none Relief: Negative, Low XP: characteristic lamellar twinning, very low, almost isotopic, birefringence

Question 36

What is this mineral?

Answer 36

Leucite

Question 37

What are the optical properties of nepheline?

Answer 37

Cleavage: Two: fair [100] and [001] PPL Colour: none Pleochroism: none Relief: None cloudy appearance hexagonal habit where euhedral XP: Low 1st order δ, lack of twinning, night sky appearance due to abundant small inclusions,

Question 38

What is leucite and where is it found?

Answer 38

Leucite occurs in alkaline igneous rocks such as syenite, phonolite, basanite, tephrite. It can occur with nepheline and sodalite. It is the principal phase within leucitites

Question 39

What is nepheline and where is it found?

Answer 39

A sodium potassium feldspathoid, the most common feldspathoid in alkaline igneous rocks such as nephelinite, nepheline syenite and phonolite; distinguished from leucite by the lower birefringence

Question 40

What is the grain size of a fine grained igneous rock?

Answer 40

\<1mm

Question 41

Where are alkaline igneous rocks formed and how do they originate?

Answer 41

Alkaline rocks are found in a wide range of tectonic environments but are particularly common in ocean islands and continental rifts Alkaline parental magmas generally originate by melting of mantle rocks at smaller degrees of partial melting or greater depth than sub-alkaline magmas

Question 42

When explaining your classification for a rock, what should you include?

Answer 42

The explanation should justify the classification in terms of rock group, phase abundance and texture.

Question 43

When writing a petrogenesis for a rock, what should you specifaically reference?

Answer 43

Minerals and textures observed in the rock

Question 44

What tectonic enironments are syenites associated with?

Answer 44

intraplate continental magmatism

Question 45

What tectonic environments are monzogranites associated with?

Answer 45

shallow level, subvolcanic acid intrusions