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Texas A&M Geology 101
Igneous Rock Samples
13
Geology
Undergraduate 1
02/06/2010

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Cards

Term

Igneous Rocks

2a - Pegmatitic Granite
Texture: Pegmatitic
Composition: Felsic

Very large crystals, in our samples there is a majority of pink, Potassium feldspar.

Definition
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Term
Igneous Rocks

1 - Diorite
Texture: Phanertic
Composition: Intermediate

About half light and half dark colored crystals.
Definition
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Term

Igneous Rocks

2b - Granite 
Texture: Phaneritic
Composition: Felsic

Crystals are visible, but are quite small.

Definition
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Term
Igneous Rocks

4 - Obsidian
Texture: Glassy
Composition: Felsic to Mafic, Dark Colored

Distinct glassy texture.
Definition
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Term
Igneous Rocks

3b - Pumice
Texture: Vesicular
Composition: Felsic to Intermediate

Very small vesicles, can be difficult to see.
Very light, floats on water.
Definition
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Term
Igneous Rocks

3a - Scoria
Texture: Vesicular
Composition: Mafic

Resembles a sponge, in our samples the holes (vesicles) are usually smaller in Scoria than in Vesicular Basalt (9a)
Definition
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Term

Igneous Rocks

6 - Peridotite 
Texture: Phaneritic
Composition: Ultramafic

Green color due to large amounts of the mineral, Olivine.

 

Definition
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Term
Igneous Rocks

5 - Rhyolite 
Texture: Aphanitic
Composition: Felsic
Definition
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Term
Igneous Rocks

8 - Gabbro 
Texture: Phaneritic
Composition: Mafic

Crystals visibl
Definition
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Term
Igneous Rocks

7 - Volcanic Tuff 
Texture: Pyroclastic
Composition: Felsic to Mafic

May appear to be Vesicular, but upon closer inspection one can see fragments of preexisting rock in the holes.
Definition
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Term
Igneous Rocks

9b - Basalt
Texture: Aphanitic
Composition: Mafic

Can not see crystals, dark grey to black color.
Definition
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Term

Igneous Rocks

9a - Vesicular Basalt 
Texture: Vesicular
Composition: Mafic

Our samples tend to have larger vesicles than scoria.

Definition
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Term
Igneous Rocks

10 - (Porphyritic) Andesite
Texture: Porphyritic or Aphanitic
Composition: Intermediate

Light gray to brown color.

If an abundant number of larger crystals (phenocrysts) are present in the fine grained ground mass, then it is a porphyritic andesite.

If phenocrysts are few a far between, it has a aphanitic texture and is simply, Andesite.
Definition
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