Day 2 Pretest

Question 1

Point Counting Method

Answer 1

A technique in petrography that involves traversing a thin section in a grid and counting minerals at each grid point to determine modal composition.

Question 2

Mode of a Rock

Answer 2

The proportion of minerals in a rock, expressed as a percentage of volume or weight.

Question 3

Becke Line Movement

Answer 3

A bright line seen around a mineral grain in a liquid of different refractive index, used to determine whether the mineral has a higher or lower RI.

Question 4

Idiochromatic Minerals

Answer 4

Minerals that exhibit color due to their inherent composition, such as Azurite (blue) and Cinnabar (red).

Question 5

Allochromatic Minerals

Answer 5

Minerals that owe their color to trace impurities or structural defects, such as Amethyst (purple quartz with iron).

Question 6

Cinnabar

Answer 6

The primary ore of mercury, composed of mercury sulfide (HgS), and known for its deep red color.

Question 7

Metamorphic Facies

Answer 7

A set of metamorphic mineral assemblages that develop under specific pressure-temperature conditions, such as greenschist and granulite facies.

Question 8

Troctolite

Answer 8

A coarse-grained, igneous rock composed primarily of olivine and plagioclase feldspar, belonging to the gabbro family.

Question 9

Pleochroism

Answer 9

The optical property where a mineral displays different colors when viewed under polarized light from different angles.

Question 10

Dichroism vs. Trichroism

Answer 10

Dichroism occurs in uniaxial minerals (two colors), while trichroism occurs in biaxial minerals (three colors).

Question 11

TAS Diagram

Answer 11

A classification diagram for volcanic rocks based on total alkali (Na₂O + K₂O) and silica (SiO₂) content.

Question 12

Undulose Extinction

Answer 12

A wavy extinction pattern observed in quartz and other minerals under a microscope, caused by strain deformation.

Question 13

Desert Rose

Answer 13

A flower-like gypsum crystal formation that occurs in arid environments due to seasonal water fluctuations.

Question 14

Solidus vs. Liquidus

Answer 14

Solidus is the temperature below which a substance is entirely solid, while liquidus is the temperature above which it is entirely liquid.

Question 15

Tie Line in Phase Diagrams

Answer 15

A horizontal line connecting two coexisting phases in equilibrium within a two-phase region of a phase diagram.

Question 16

Melatope

Answer 16

The narrowest part of an isogyre in an interference figure, representing the point where an optic axis emerges.

Question 17

Isogyre vs. Isochrome

Answer 17

Isogyre refers to dark cross patterns in an interference figure, while isochrome refers to colored concentric rings.

Question 18

Adularia

Answer 18

A potassium feldspar that forms in low-temperature hydrothermal veins and resembles microcline but lacks tartan twinning.

Question 19

Peridotite

Answer 19

A coarse-grained ultramafic rock composed mostly of olivine, with varying amounts of pyroxene and hornblende.

Question 20

Botryoidal Texture

Answer 20

A mineral habit resembling a cluster of grapes, commonly seen in hematite and malachite.

Question 21

Geode

Answer 21

A hollow rock formation lined with mineral crystals, typically formed in volcanic or sedimentary rocks.

Question 22

Monzonite

Answer 22

An intrusive igneous rock containing nearly equal amounts of potassium feldspar and plagioclase feldspar.

Question 23

Norite

Answer 23

A type of gabbro rich in orthopyroxene, commonly associated with layered mafic intrusions.

Question 24

Eutectic Point

Answer 24

The lowest temperature at which a mixture of components can melt simultaneously, forming a single liquid phase.

Question 25

Peritectic Reaction

Answer 25

A reaction where a solid and a liquid combine to form a new solid at a specific temperature.

Question 26

Miscibility Gap

Answer 26

A region in a phase diagram where two immiscible phases coexist instead of forming a homogeneous mixture.

Question 27

Plagioclase Feldspar

Answer 27

A solid solution series between albite (NaAlSi₃O₈) and anorthite (CaAl₂Si₂O₈) found in igneous rocks.

Question 28

Metamorphic Rock Progression

Answer 28

Foliated metamorphic rocks progress from slate to phyllite, schist, gneiss, and granulite with increasing metamorphism.

Question 29

Udden-Wentworth Scale

Answer 29

A grain size classification system for sediments, ranging from clay to boulders.

Question 30

Miller Indices

Answer 30

A system used to describe the orientation of crystal planes in a crystal lattice.

Question 31

Interference Colors

Answer 31

Colors seen in thin sections under cross-polarized light due to variations in birefringence.

Question 32

Extinction Types

Answer 32

Parallel extinction occurs when a mineral goes dark along cleavage planes, while inclined extinction occurs at an angle.

Question 33

Crystal Forms

Answer 33

General forms are defined by Miller Indices {hkl}, while special forms are unique to specific crystal classes.

Question 34

Twin Laws

Answer 34

Common twin laws include Albite twinning in plagioclase, Carlsbad twinning in orthoclase, and Japan Law in quartz.

Question 35

Beryl Varieties

Answer 35

Beryl occurs in different colors: Emerald (green), Aquamarine (blue), Heliodor (yellow), and Morganite (pink).

Question 36

Radioactive Minerals

Answer 36

Common uranium-bearing minerals include Autunite, Torbernite, and Uraninite.

Question 37

Motif & Unit Cell

Answer 37

A motif is a repeating atomic arrangement, while a unit cell is the smallest repeating structure of a lattice.

Question 38

Folk’s Classification of Carbonates

Answer 38

A classification for limestones based on allochems (grains) and matrix/cement (micrite, sparite).

Question 39

Index Minerals of Metamorphism

Answer 39

Chlorite (low grade), Biotite, Garnet, Staurolite, and Sillimanite (high grade) indicate metamorphic conditions.