Classification of Igneous rocks (Fabric and texture)

Question 1

Encompasses non-compositional properties of a rock that comprise textures and generally large-scale structures

Answer 1

Fabric

Question 2

based on the proportions of glass relative to mineral grains and their sizes, shapes, and mutual arrangements that are observable on the scale of a hand specimen or thin section under the microscope.

Answer 2

Texture

Question 3

Texture is also called

Answer 3

microstructures

Question 4

larger-size features generally seen in an outcrop, such as bedding in pyroclastic rocks or pillows in a submarine lava flow.

Answer 4

Structures

Question 5

very fine-grained as a result of rapid cooling at the surface. Minerals too small to be seen by the naked eye

Answer 5

Aphanitic

Question 6

coarse-grained mineral sizes due to magma cooling at depth.

Answer 6

Phaneritic

Question 7

very large crystals (phenocrysts) embedded in smaller crystals (groundmass)

Answer 7

Porphyritic

Question 8

contain variable proportion of glass; molten rock quenched quickly as it was ejected into the atmosphere

Answer 8

Glassy or vitric

Question 9

a highly viscous liquid, disordered on the atomic scale, formed from polymerized silicate melt

Answer 9

Glass

Question 10

a porphyritic rock that contains scattered phenocrysts in a glassy matrix.

Answer 10

Vitrophyre

Question 11

produced by fragmenting processes that create broken pieces of volcanic rock and/or mineral
grains.

Answer 11

Volcaniclastic/Pyroclastic

Question 12

Degree of crystallinity wherein its wholly crystalline texture

Answer 12

Holocrystalline

Question 13

Degree of crystallinity wherein its partially crystalline/partially glass texture

Answer 13

Hypocrystalline

Question 14

Degree of crystallinity wherein its wholly glassy textures

Answer 14

Holohyaline

Question 15

A crystal form where the crystal is bounded by faces; developed under circumstances such as slow cooling of magma in a deep-seated condition.

Answer 15

Euhedral /idiomorphic

Question 16

Crystal form: an intermediate stage of development

Answer 16

Subhedral

Question 17

crystal faces are absent; developed as the growth of crystals has been hindered by such factors as disturbing environment, reaction with magma, and juxtaposition of other growing crystals.

Answer 17

Anhedral/xenomorphic

Question 18

mix of euhedral, subhedral and anhedral grains

Answer 18

Hypidiomorphic-granular texture

Question 19

A massive, high silica glass appears in hand samples to have zero crystallinity. Under the microscope, high magnification reveals that obsidian contains abundantly nucleated submicrometer-size crystallites that experienced limited growth in the highly viscous glass.

Answer 19

Obsidian

Question 20

Important alteration product of devitrification

Answer 20

Palagonite

Question 21

Product of devitrification; spherulites are spherical to ellipsoidal clusters of radiating fibrous alkali feldspars and a polymorph of SiO2.

Answer 21

Spherulitic texture

Question 22

massive glass having a waxy luster and dark color in hand sample into which 6-16 wt% water has been absorbed

Answer 22

Pitchstone

Question 23

develops by the hydration of obsidian on fracture surfaces that are exposed to moisture in the atmosphere or to meteoric water (groundwater).

Answer 23

Perlitic texture

Question 24

characterized by large crystals averaging more than 30 mm in diameter. it displays large, early-formed euhedral crystals surrounded by later-formed subhedral crystals.

Answer 24

Pegmatitic texture

Question 25

refers to extremely fine-grained minerals.

Answer 25

APLITIC TEXTURE

Question 26

contain spherical to ellipsoidal void spaces called vesicles, which are analogous to holes in a household sponge

Answer 26

Vesicular textures

Question 27

develop due to the exsolution and entrapment of gas bubbles in lava as it cools and solidifies.

Answer 27

Vesicular textures

Question 28

phenocrysts are found to occur as clusters of crystals

Answer 28

Glomeroporphyritic

Question 29

vesicles have been filled with material (usually calcite, chalcedony, or quartz, then the term amygdular should be added to the textural description of the rock

Answer 29

Amygdular

Question 30

vesicles are so abundant that they make up over 50% of the rock and the rock has a density of less than 1 (i.e. it would float in water)

Answer 30

Pumiceous

Question 31

vesicles are so abundant that they make up over 50% of the rock and the rock has a density greater than 1,

Answer 31

Scoriaceous-

Question 32

a texture consisting of intergrowths of quartz and alkali feldspar wherein the orientation of the quartz grains resembles cuneiform writing. This texture is most commonly observed in pegmatites.

Answer 32

Graphic

Question 33

a texture commonly found in glassy rhyolites wherein spherical intergrowths of radiating quartz and feldspar replace the glass as a result of devitrification.

Answer 33

Spherulitic

Question 34

a texture usually restricted to coarser-grained rocks that consist of concentrically banded spheres wherein the bands consist of alternating light-colored and dark-colored minerals.

Answer 34

Obicular

Question 35

an intergrowth of quartz and plagioclase that shows small wormlike bodies of quartz enclosed in plagioclase. This texture is found in granites

Answer 35

Myrmekitic texture

Question 36

laths of plagioclase in a coarse-grained matrix of pyroxene crystals wherein the plagioclase is totally surrounded by pyroxene grains. This texture is common in diabases and gabbros.

Answer 36

Ophitic texture

Question 37

similar to ophitic texture wherein the plagioclase grains are not completely enclosed in a matrix of pyroxene grains.

Answer 37

Subophitic texture

Question 38

smaller grains of one mineral is completely enclosed in large, optically continuous grains of another mineral.

Answer 38

Poikilitic texture

Question 39

A texture in which the angular interstices between plagioclase grains are occupied by grains of ferromagnesium minerals such as olivine, pyroxene, or iron titanium oxides

Answer 39

Intergranular texture

Question 40

a texture similar to intergranular texture except that the Interstices between plagioclase grains are occupied by the glass or cryptocrystalline material.

Answer 40

Intersertal texture

Question 41

a texture similar to ophitic texture except that glass completely surrounds the plagioclase laths.

Answer 41

Hyaloophitic texture

Question 42

a texture wherein microlites of plagioclase are more abundant than groundmass and the groundmass consists of glass which occupies the tiny interstices between plagioclase grains

Answer 42

Hyalopilitic texture

Question 43

A texture wherein plagioclase grains show a preferred orientation due to flowage and the interstices between plagioclase grains are occupied by the glass or cryptocrystalline material.

Answer 43

Trachytic texture

Question 44

this texture surround individual crystals as a result of the crystal becoming unstable and reacting with its surroundingcrystals or melt.

Answer 44

Coronas or reaction rims

Question 45

occurs in plagioclase crystals where irregularly shaped patches of the crystal show different compositions as evidenced by going extinct at angles different from other zones in the crystal.

Answer 45

Patchy zoning

Question 46

occurs in plagioclase grains wherein concentric zones around the grain show thin zones of different compositions as evidenced by extinction phenomena.

Answer 46

Oscillatory zoning

Question 47

This sometimes occurs in plagioclase wherein individual plagioclase grains show an abundance of glassy inclusions.

Answer 47

Moth eaten texture

Question 48

Moth-eaten texture is also known as

Answer 48

Sieve texture

Question 49

Exsolution lamellae of albite occurring in orthoclase or microcline

Answer 49

Perthitic texture

Question 50

a term used to describe grains with rectangular tablet shapes.

Answer 50

Tabular

Question 51

a term used to describe grains that have all of their boundaries of approximately

Answer 51

Equant

Question 52

a term used to describe grains that occur as long fibers

Answer 52

Fibrous

Question 53

a term used to describe grains that occurs as long, slender crystals.

Answer 53

Acicular

Question 54

A term used to describe grains that show an abundance of prism faces.

Answer 54

Prismatic