Imperial College Rock Library

Glossary: Glomeroporphyritic

Synonyms: glomerophyric
    Glomeroporphyritic is a term used to describe a porpyritic texture in which phenocrysts are clustered into aggregates called glomerocrysts or crystal clots. Glomeroporphyritic textures are common and often included plagioclase and pyroxenes in basic rocks. They form by a processes known as synneusis, where accumulation of crystals occurs by surface tension and fixing by interpenetration due to crystal growth.
Glomerocrysts are an important consideration in crystal fractionation by crystal settling since the density of the glomerocryst is an average of that of its constituent phases. Formation of glomerocrysts may in part explain the settling of plagioclase in basic intrusions in which plagioclase crystals are less dense than the surrounding magma.
Glomeroporphyritic textures are particularly common in andesites and dacites. Leucite in leucitites also commonly forms large glomerocrysts.

Related Terms

porphyritic, synneusis

Example Images

A XPL image showing a glomerop... view   view rock

A XPL view showing altered oli... view   view rock

A PPL view showing altered oli... view   view rock

A XPL view showing a glomeropo... view   view rock

A XPL image of a thin section ... view   view rock
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