Felsite

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Felsite covered with dendritic pyrolusite formations.

Felsite is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light grey, reds to tan and may include any color except dark grey, green or black (the colors of traprock).^[1] The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of volcanic origin, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools.