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rocks masterclass > rocks > Flashcards

rocks Flashcards

1
Q

What are the most common and important minerals?

A

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

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2
Q

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

A

zircon, apatite, titanite, rutile (accessories)

cordierite (mostly granites)

leucite, nepheline (alkali igneous; feldspathoids)

tremolite, actinolite, epidote, serpentine (alterations)

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3
Q

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

A

staurolite, andalucite, kyanite, sillimanite, cordierite,

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

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4
Q

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

A

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

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5
Q

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

A

Quartz and feldspar (leucocratic)

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6
Q

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

A

Plag = mafics (50:50)

Hornblende common but can be pyroxene (mesocratic)

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7
Q

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

A

Plag + Pyroxene (melanocratic)

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8
Q

What minerals characterise ultrabasic igneous rocks?

A

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

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9
Q

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

A

Cordierite, Andalusite

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10
Q

What index minerals characterize the Greenschist facies?

A

Garnet, Chlorite and Biotite

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11
Q

What index minerals characterize the Amphibolite facies?

A

Staurolite, Kyanite, Sillimanite

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12
Q

What minerals are indicative of a Blueschist facies rock?

A

Glaucophane and lawsonite

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13
Q

What minerals are indicative of a Eclogite facies rock?

A

Garnet and omphacite

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14
Q

What’s the field of view on x4 magnification?

A

4.4mm

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15
Q

What’s the field of view on x10 magnification?

A

1.8mm

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16
Q

What’s the field of view on x40 magnification

A

0.4mm

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17
Q

What grain size is a medium grained igneous rock?

A

1mm-3mm

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18
Q

What grain size is a coarse grained igneous rock?

A

3mm-3cm

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19
Q

What grain size is a very coarse grained igneous rock?

A

>3cm

20
Q

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

A

Sanidine

21
Q

What are the optical properties of sanidine?

A

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

22
Q

What is the difference between cpx and opx?

A

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

23
Q

What is the difference between an amphibole and a px?

A

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.

24
Q

What is the distinguishing feature of titanite?

A

Lozenge shaped

25
Q

What is the distinguishing feature of zircon?

A

Forms pleochroic haloes in biotite

26
Q

Chiastolite is a type of what?

A

Andalusite

27
Q

What are the distinguishing features of Andalusite?

A

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

28
Q

What are the distinguishing features of Kyanite?

A

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

29
Q

In what rock is sanidine most likely to be found?

A

Sanidine is a high temperature, potassium-rich alkali feldspar, Typically forms tabular laths,

Occurs in silicic lavas (rapidly cooled igneous rocks)

30
Q

What are the distinguishing features of olivine?

A

PPL: High relief, curved fractures, weathering (serpentine, iddingsite)

XP: 2nd – 3rd order δ

31
Q

What are the distinguishing features of Sillimanite?

A

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

32
Q

What are the distinguishing features of Garnet?

A

PPL: High relief, colourless to pale pink

XP: Isotropic (because cubic), often poikilitic

33
Q

What are the distinguishing features of cordierite?

A

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)

34
Q

What are the distinguishing features of staurolite?

A

PPL: Almost always has honey yellow colour, strong pleochroism

XP: Low order δ colours masked by body colour

35
Q

What are the optical properties of lecite?

A

cleavage: none: very poor

PPL Colour: colourless

Pleochroism: none

Relief: Negative, Low

XP: characteristic lamellar twinning, very low, almost isotopic, birefringence

36
Q

What is this mineral?

A

Leucite

37
Q

What are the optical properties of nepheline?

A

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,

38
Q

What is leucite and where is it found?

A

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

39
Q

What is nepheline and where is it found?

A

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

40
Q

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

A

<1mm

41
Q

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

A

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

42
Q

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

A

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

43
Q

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

A

Minerals and textures observed in the rock

44
Q

What tectonic enironments are syenites associated with?

A

intraplate continental magmatism

45
Q

What tectonic environments are monzogranites associated with?

A

shallow level, subvolcanic acid intrusions

rocks masterclass (1 decks)

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