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Abstract

Petrographic analysis using a polarizing microscope was carried out to determine the texture and minerals of Mount Gamalama's lava in North Maluku, Indonesia. Microscopic observations were made on seventeen representative samples. The results of these observations indicate that in general the lava is classified as an extrusive rock in the form of basalt. The mineral composition of the lava consists of phenocryst plagioclase and pyroxene set in the groundmass of needles and plagioclase microlites, pyroxene, opaque minerals and volcanic glass. Sericite mineral and iron oxide occur as secondary minerals. The general textures of the rock are micro aphanitic porphyry, inequigranular, and vesicular, while the special textures found are hyalopilitic, glomeroporphyritic, oscillatory zoning, and sieve.