Petrology and Optical Features

Question 1

Formation of rational symmetry intergrowth of 2 or more grains of crystalline species.

Answer 1

Twinning

Question 2

Form of penetration twinning where two
crystals form as penetration twins.

Answer 2

Carlsbad Twining

Question 3

common within the plagioclase feldspars, in places where two adjoining twin slabs or lamellae are mutually reversed with respect to each other and every alternate twin ‘plate’ or ‘slab’ has an identical atomic structure

Answer 3

Lamellar Twining

Question 4

shows two kinds of repeated twinning in thin section, with one set of twins arranged at 90° to the other set.

Answer 4

Cross-hatched twinning

Question 5

Refers to solid solution which do not have uniform composition.

Answer 5

Zoning

Question 6

Types of Zoning

Answer 6

Normal Zoning
Reverse Zoning
Oscillatory Zoning

Question 7

Types of Zoning where the center is more calcic becoming more sodic toward the margin

Answer 7

Normal Zoning

Question 8

Types of Zoning where the center is more sodic becoming more calcic toward the margin.

Answer 8

Reverse Zoning

Question 9

Types of Zoning that is normally steplike progressions for more calcic interior to more sodic margins w/ local reversals in adjacent zones

Answer 9

Oscillatory Zoning

Question 10

it is when a mineral becomes dark parallel to the crosshairs.

Answer 10

Parallel Extinction

Question 11

Extinct at an angle
with the direction of polars

Answer 11

Inclined/Oblique

Question 12

planes of mineral to the diagonal; vibration direction is diagonal

Answer 12

Symmetrical

Question 13

phenocrysts lie in a matrix of glass.

Answer 13

Vitrophyric Texture

Question 14

the groundmass is a dense intergrowth of quartz and feldspar.

Answer 14

Felsophyric Texture

Question 15

the groundmass of feldspar are rectangular in form instead of slender lath crystals

Answer 15

Orthopyric Texture

Question 16

porpyritic texture in which phenocrysts are clustered into aggregates called glomerocrysts or crystal clots. It is common and often included plagioclase and pyroxenes in basic rocks.

Answer 16

Glomeroporphyritic Texture

Question 17

an important consideration in crystal fractionation by crystal settling

Answer 17

Glomerocrysts

Question 18

Refers to crystals, typically phenocrysts, in an igneous rock which contain small grains of other minerals.

Answer 18

Poikilitic Texture

Question 19

A variant the Poikilitic texture, is one where random plagioclase laths are enclosed by pyroxene or olivine.

Answer 19

Ophitic Texture

Question 20

A variant the Poikilitic texture,** plagioclase is larger and encloses the ferromagnesian minerals.**

Answer 20

Sub-ophitic

Question 21

Angular interstices between feldspars filled with glass instead of pyroxene

Answer 21

Hyalophitic Texture

Question 22

A genetic term for a border of secondary minerals formed at the margin of a primary grain in an igneous or metamorphic rock.

Answer 22

Corona Texture/ Reaction Rim /
Opacitic Rim

Question 23

Secondary rim/coronas

Answer 23

Kelyphitic Rim

Question 24

a textural term indicating that** a crystal occupies the angular space between at least two larger crystals.**

Answer 24

Intergranular Texture

Question 25

A textural term used to denote that the **angular spaces** between larger crystals is **occupied by glass, or glass and small crystals.**

Answer 25

Intersertal Texture

Question 26

Texture of the groundmass of a holocrystalline igneous rock in which** lath-shaped microlites (typically plagioclase) are arranged in a glass-free mesostasis** and are** generally interwoven in irregular unoriented fashion**.

Answer 26

Pilotaxitic Texture

Question 27

A texture of extrusive rocks in which the **groundmass contains little volcanic glass and consists predominantly of minute tabular crystals**, namely, sanidine microlites.

Answer 27

Trachytic Texture

Question 28

An **intergrowth of branching rods of quartz set in a single crystal of plagioclas**e, neighboring rod of quartz have the same lattice orientation and extinguish together.

Answer 28

Myrmekitic Texture

Question 29

________________ commonly exhibits a variety of disequilibrium textures in volcanic rocks, especially in orogeny andesites

Answer 29

Plagioclase

Question 30

common in plagioclase or in pyroxene crystals in extrusive volcanic rocks and is interpreted as the result of mixing processes

Answer 30

Sieve Texture

Question 31

A process by which a solid solution phase unmixes into two separate phases in the solid state.

Answer 31

Exsolution

Question 32

an intimate intergrowth of sodic and potassic feldspar resulting from subsolidus exsolution

Answer 32

Perthitic Texture

Question 33

an intergrowth arising due to exsolution where potassic feldspar is present as blebs or lamellae within a sodic feldspar.

Answer 33

Anti-PerthicTexture

Question 34

Chiefly minerals are anhedral. and are common in aplites

Answer 34

Saccharoidal/ Aplitic

Question 35

chiefly minerals are euhedral and are common in dark hypabyssal rocks or lamprophyres

Answer 35

Lamprophyric

Question 36

all faces are present

Answer 36

Granitic

Question 37

Extremely minute, incipient crystals, provided they are birefringent.

Answer 37

Microlites

Question 38

Smaller, spherical, rod- and hair-like isotropic from.

Answer 38

Crystallite

Question 39

refers to degree of crystallinity, grain size or granularity, and the fabric or geometrical relationship between the constituents of a rock.

Answer 39

Texture

Question 40

what are the Degree of crystallinity

Answer 40

Holocrystalline Holohyaline Hypocrystalline/Merocrystalline

Question 41

consist entirely of glass

Answer 41

Holohyaline

Question 42

consist wholly of crystals

Answer 42

Holocrystalline

Question 43

Contain both crystals and glass

Answer 43

Hypocrystalline/Merocrystalline

Question 44

Crystals were bounded completely by crystal faces.

Answer 44

Euhedral / Idiomorphic / Automorphic

Question 45

Crystals were not bounded by crystal faces.

Answer 45

Anhedral / Allotriomorphic / Xenomorphic

Question 46

Crystals were partially bounded by crystal faces

Answer 46

Subhedral / Hypidiomorphic