leaverites - Features in Igneous Rocks

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, Universityof Wisconsin - Green Bay

Phenocrysts

Large crystals in an otherwise fine-grained rock

Streaks due to flow of lava or magma

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.

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

Rubbly surface texture on lava flows

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

Created 22 April, 2005, Last Update