mineral
Drusy quartz coating on volcanic rock
Quartz (SiO₂), likely druzy quartz on basalt or another mafic host
AI-generated identification · may be incorrectTiny sparkling quartz crystals form a dark gray to purple granular surface over a dense, darker rock. Quartz hardness is 7 Mohs, vitreous luster, trigonal crystal structure, and no cleavage; the host appears fine-grained and may be basaltic.
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Physical properties
Tiny sparkling quartz crystals form a dark gray to purple granular surface over a dense, darker rock. Quartz hardness is 7 Mohs, vitreous luster, trigonal crystal structure, and no cleavage; the host appears fine-grained and may be basaltic.
Formation & geological history
Groundwater or hydrothermal fluids deposited microcrystalline quartz in cavities or along fractures, commonly during cooling or later alteration of volcanic rock. The precise age and locality cannot be determined from the image.
Uses & applications
Used as a decorative and collecting specimen; attractive drusy surfaces may be incorporated into jewelry and polished décor. The host rock has little industrial value in this form.
Geological facts
The glitter comes from many crystal faces rather than metallic particles. Purple coloration may indicate amethyst-bearing quartz or surface staining, but the image is insufficient for confident identification.
Field identification & locations
Look for a sugary, sparkly quartz surface, glassy crystal reflections, and a hard, nonmetallic coating; a scratch test should not mark quartz with a steel nail. Common examples occur in volcanic cavities worldwide, especially Brazil, Uruguay, Mexico, and Morocco.
