Vesicular texture

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Vesicular olivine basalt
A volcanic sand grain with many vesicles, viewed with a petrographic microscope. Scale box in millimeters.

Vesicular texture is a volcanic rock texture characterized by a rock being pitted with many cavities (known as vesicles) at its surface and inside.[1] The texture is often found in extrusive aphanitic, or glassy, igneous rock. These vesicles form during the extrusion of magma to the surface; as the pressure decreases, dissolved magmatic gases are able to come out of solution, forming gas bubbles (the cavities) in the magma. When the magma is extruded as lava and cools, the lava solidifies around the gas bubbles, preserving them as vesicles.[2]

A related texture is amygdaloidal in which the volcanic rock, usually basalt or andesite, has cavities, or vesicles, that are filled with secondary minerals, such as zeolites, calcite, quartz, or chalcedony. Individual cavity fillings are termed amygdules (American usage), or amygdales (British usage). Sometimes these can be sources of semi-precious stones such as agate.

Rock types that display a vesicular texture include pumice and scoria.

Notes[edit]

  1. ^ See "Elmhurst College Powerpoint via google viewer", retrieved May 8, 2011
  2. ^ D. Armstrong, F. Mugglestone, R. Richards and F. Stratton "OCR AS and A2 Geology". Pearson Education Limited, 2008, p. 76.