Leaverites - Features in Igneous Rocks

Steven Dutch, Natural and Applied Sciences, University of Wisconsin - Green Bay
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Phenocrysts

Large crystals in an otherwise fine-grained rock

Flow Banding

Streaks due to flow of lava or magma

Vesicles

Vesicle is the generic term for cavities due to gas bubbles in the lava (rarely, magma)

The cavities in this specimen of obsidian are lined with a form of silica called cristobalite. The cavities are called lithophysae.

Almond-shaped cavities in basalt are called amygdules and the texture is called amygdaloidal. The cavities may be empty or filled with minerals.

Pillow Lava

Rounded masses of lava caused by sudden cooling upon contact with water. These are in Olympic National Park, Washington
This outcrop of pillow lava in Scotland has been eroded by waves.
Precambrian pillow lava in Ontario. The outcrop has been planed off by glaciation.

 

Pahoehoe

Ropy surface texture on lava flows

Aa

Rubbly surface texture on lava flows

Orbicular texture

Round clusters of crystals, sometimes with a bulls-eye pattern, in granite

 


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Created 22 April, 2005, Last Update 14 December 2009

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