Lava From The Soufriere Hills Volcano Essay

2349 Words Dec 1st, 2014 null Page
The lava from the Soufriere Hills volcano is a porphyritic andesite with 35 to 45 weight percent in phenocrysts (Voight et al., 1999). The phenocrysts in the lava are composed of different minerals such as; plagioclase, hornblende, orthopyroxene, titano-magnetite and less than five weight percent of quartz (Voight et al., 1999). The groundmass of the lava is comprised of plagioclase, orthopyroxene, clinopyroxenes, Iron and Titanium oxides, glass, and silica mineral (Voight et al., 1999) The glass found within the groundmass is a high silica rhyolite glass that varies in content from 25 to 30 weight percent (Voight et al., 1999) The silica minerals in the lava, specifically in the glass, were produced by vapor phase crystallization as well as devitrification within the dome that occurred in the dome for a period of many days to several weeks (Voight et al., 1999).

The plagioclase within the magma ranges in size from small microlites to large phenocrysts and are comprised of four main plagioclase types that are distinguished by composition, zoning patterns as well as textures (Murphy et al., 1999). The first type of plagioclase found is known as sodic phenocrysts with contain oscillatory zoning (Murphy et al., 1999). The second type of plagioclase is reverse zoned large sodic phenocrysts and microphenocrysts that also have oscillatory zoned cores (Murphy et al., 1999). The third type of plagioclase is reverse zoned dusty sieve-textured crystals that have clear…

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