Igneous Rocks

Front 1

phaneritic vs. aphanitic

Back 1

phaneritic - grains of size which can be distinguished with the naked eye

aphanitic - grains cannot be distinguihsed w/naked eye

Front 2

intrusive vs. extrusive

Back 2

intrusive - crystallization occured very rapidly above the surface of the earth, resulting in small grain size

extrusive - crystallization occured below the surface of the earth, allowing the material to cool slowly, bigger grains

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Back 3

Colour: dark grey, greenish, brownish.

Mineralogy: essential plagioclase and pyroxene, other minerals include olivine, hornblende, spinel, ilmenite, magnetite, apatite.

Classification: basic plutonic igneous rock.

Occurrence: deeper continental crust, widespread.

Texture: course grained, granitic texture, crystals intergrown; may have lath like crystals of feldspar aligned parallel to layering.

Structure: commonly layered, may show alternating light (feldspar rich) and dark (pyroxene and/or olivine) layers.

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Back 4

Colour: colourless grains, also mottled in white, pink or red, some grey or dark grains.

Mineralogy: essential quartz, alkali feldspar and plagioclase in variable amounts, usually with hornblende and/or biotite; muscovite may occur.

Classification: acid plutonic igneous rock.

Occurrence: intrusive, most commonly occurring in batholiths.

Texture: coarse to very coarse-grained; usually granular; may be porphyritic with well-shaped phenocrysts (large crystals) of feldspar; sometimes foliated; coarse intergrowths of quartz and feldspars can form a ‘graphic’ texture.

Front 5

pyroclastic?!

Back 5

Pyroclastic means ‘fire-broken’, a name for rocks that have been blown apart by exploding gases.

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Back 6

Colour: white or grey powder when newly fallen.

Composition: ash-fall tuffs composed of a mixture of rock fragments, crystals and glass shards.

Classification: pyroclastic igneous rock.

Occurrence: associated with explosive volcanic activity, particle size decreases away from the vent because lighter ash is carried further by the wind.

Texture: fine-grained, less than 2mm.

Structure: ash-fall tuffs are often well-bedded.

Front 7

Back 7

rhyolite
aphanitic kspar felsic rock quartz

Front 8

Back 8

oegmatitic granite
large crystals

Front 9

porphyrytic

Back 9

Porphyritic- Mixture of grain sizes caused by mixed cooling history; slow cooling first, followed by a period of somewhat faster cooling.

Front 10

phenocrysts vs. groundmass

Back 10

large crystals vs. small crystals in porphyritic rocks

Front 11

Igneous volcanic properties

Back 11

-numerous bubble like cavities that may or may not be lined with nminerals
-has obvious bubbly or frothy texture
-is fine-grained, uniform in texture, and hard
-glassy or highly vesicular rocks are almost always igneous

Front 12

igneous plutonic properties

Back 12

made of discrete mineral grains locked together

contains large crystals in a finer grained mass

rock mass obviously cuts across other rock structures