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Geology Board Exam Day 2 > Classification of Igneous rocks (Fabric and texture) > Flashcards

Classification of Igneous rocks (Fabric and texture) Flashcards

1
Q

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

A

Fabric

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2
Q

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.

A

Texture

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3
Q

Texture is also called

A

microstructures

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4
Q

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

A

Structures

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5
Q

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

A

Aphanitic

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6
Q

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

A

Phaneritic

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7
Q

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

A

Porphyritic

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8
Q

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

A

Glassy or vitric

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9
Q

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

A

Glass

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10
Q

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

A

Vitrophyre

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11
Q

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

A

Volcaniclastic/Pyroclastic

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12
Q

Degree of crystallinity wherein its wholly crystalline texture

A

Holocrystalline

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13
Q

Degree of crystallinity wherein its partially crystalline/partially glass texture

A

Hypocrystalline

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14
Q

Degree of crystallinity wherein its wholly glassy textures

A

Holohyaline

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15
Q

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

A

Euhedral /idiomorphic

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16
Q

Crystal form: an intermediate stage of development

A

Subhedral

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17
Q

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.

A

Anhedral/xenomorphic

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18
Q

mix of euhedral, subhedral and anhedral grains

A

Hypidiomorphic-granular texture

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19
Q

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.

A

Obsidian

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20
Q

Important alteration product of devitrification

A

Palagonite

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21
Q

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

A

Spherulitic texture

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22
Q

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

A

Pitchstone

23
Q

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

A

Perlitic texture

24
Q

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

A

Pegmatitic texture

25
Q

refers to extremely fine-grained minerals.

A

APLITIC TEXTURE

26
Q

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

A

Vesicular textures

27
Q

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

A

Vesicular textures

28
Q

phenocrysts are found to occur as clusters of crystals

A

Glomeroporphyritic

29
Q

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

A

Amygdular

30
Q

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)

A

Pumiceous

31
Q

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

A

Scoriaceous-

32
Q

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.

A

Graphic

33
Q

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

A

Spherulitic

34
Q

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.

A

Obicular

35
Q

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

A

Myrmekitic texture

36
Q

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.

A

Ophitic texture

37
Q

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

A

Subophitic texture

38
Q

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

A

Poikilitic texture

39
Q

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

A

Intergranular texture

40
Q

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

A

Intersertal texture

41
Q

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

A

Hyaloophitic texture

42
Q

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

A

Hyalopilitic texture

43
Q

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.

A

Trachytic texture

44
Q

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

A

Coronas or reaction rims

45
Q

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.

A

Patchy zoning

46
Q

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

A

Oscillatory zoning

47
Q

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

A

Moth eaten texture

48
Q

Moth-eaten texture is also known as

A

Sieve texture

49
Q

Exsolution lamellae of albite occurring in orthoclase or microcline

A

Perthitic texture

50
Q

a term used to describe grains with rectangular tablet shapes.

A

Tabular

51
Q

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

A

Equant

52
Q

a term used to describe grains that occur as long fibers

A

Fibrous

53
Q

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

A

Acicular

54
Q

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

A

Prismatic

Geology Board Exam Day 2 (17 decks)

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