Igneous Rock Quiz GEOL 110L

Aphanitic

Small crystals (snickerdoodles)

Vesicular

Holes (cutout cookies)

Pyroclastic

Holes and shards, from explosive material (kitchen sink cookies)

Glassy

No crystals (sugar cookie)

Phaneritic

Medium crystals (chocolate chip cookies)

Pegmatitic

Big crystals (peanut blossom cookies)

Porphyritic

Two crystal sizes, big crystals embedded in smaller ones (oatmeal raisin cookies)

Felsic

Crystallizes at low temps, light color, high in Si, low in Fe and Mg, continental crust

Intermediate

In between felsic and mafic, two materials mixed together, continental crust caused by mixed crusts

Mafic

Crystallizes at higher temps, dark color, low in Si, high in olivine and pyroxene, ocean crust

Ultramafic

Mafic with <10 feldspar, almost pure olivine

Intrusive (below surface) textures

Phaneritic, pegmatitic, porphyritic

Extrusive (above surface) textures

Aphanitic, vesicular, pyroclastic, glassy

Convergent collision

Two plates on top of the continental crust, not deep enough to melt

Heat melting

Pocket of magma on surface, melted by heat from under continental crust, can make volcano

Convergent subduction

One oceanic crust plate slides below a continental crust plate, can melt

Flux melting

In convergent subduction, water is brought down with melting plate and creates a chemical reaction

Divergent

Plates spread apart, can melt

Decompression melting

Rock diverges, allowing mafic rock below surface to melt, can make volcano

Obsidian

• Glassy

• Felsic

• Extrusive

• Continental crust, at surface of volcano

Peridotite

• Phaneritic

• Ultramafic

• Intrusive

• Ocean crust, below lithosphere

Scoria

• Vesicular

• Mafic

• Extrusive

• Ocean crust, at surface of volcano

Granite

• Pegmatitic or phaneritic

• Felsic

• Intrusive

• Continental crust, within the crust or middle of volcano

Aphanitic basalt

• Aphanitic

• Mafic

• Extrusive

• Ocean crust, at surface of crust

Vesicular basalt

• Vesicular

• Mafic

• Extrusive

• Ocean crust, at surface of volcano

Andesite

• Porphyritic, big crystals within aphanitic

• Intermediate

• Extrusive

• Continental crust, at surface of volcano

Pumice

• Vesicular

• Felsic

• Extrusive

• Continental crust, at surface of volcano

Gabbro

• Phaneritic

• Mafic

• Intrusive

• Ocean crust, within the crust

Diorite

• Phaneritic

• Intermediate

• Intrusive

• Continental crust, within the crust or in the volcano

Rhyolite

• Aphanitic

• Felsic

• Extrusive

• Continental crust, at surface of volcano

Tuff

• Pyroclastic

• Felsic

• Extrusive

• Continental crust, at surface of volcano