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| VESICULAR BASALT
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Typical Minerals Minerals too small to identify (except phenocrysts). Composition will be from the top of Bowen's Reaction series (i.e. mafic) and we would expect Ca plagioclase, pyroxene, and perhaps some olivine. This specimen is approaching scoria and may in fact not have any minerals, being a glass instead.
| Description
This vesicular or cellular specimen was produced when gas expanded as the lava was extruded to the surface. The fact that the lava was still fluid and moving can be seen by the fact the vesicles are all stretched out in the same direction. This rock is probably close to being scoria, meaning it is the result of very fast cooling.
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Tectonic Association
Basalt is one of the most common igneous rocks found. It is the major constituent of the upper layer of the ocean floors (usually as pillow lava), and hot spot volcanoes (such as the Hawaiian islands). Vesicular varieties such as this one are typically terrestrial, forming either on volcanic islands or on the continents.
 Tectonic Cross Section - pdf version
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| Last Update: 9/29/00 | e-mail: (Fichtels@jmu.edu) |