mineral
Botryoidal chalcedony (likely druzy quartz)
Microcrystalline quartz, SiO₂; chalcedony with a druzy quartz coating
AI-generated identification · may be incorrectGray to blue-gray, waxy to vitreous luster with sparkling microscopic quartz crystals and rounded botryoidal surfaces; hardness about 6.5–7 Mohs, trigonal quartz structure, no cleavage, specific gravity about 2.6. The exact species is uncertain from the photograph alone.
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Physical properties
Gray to blue-gray, waxy to vitreous luster with sparkling microscopic quartz crystals and rounded botryoidal surfaces; hardness about 6.5–7 Mohs, trigonal quartz structure, no cleavage, specific gravity about 2.6. The exact species is uncertain from the photograph alone.
Formation & geological history
Silica-rich groundwater deposited layers of chalcedony and quartz in cavities, vesicles, or fractures, commonly in volcanic rocks; age depends on its host deposit and may range from young hydrothermal material to ancient volcanic formations.
Uses & applications
Used as a lapidary specimen, cabochon, ornamental stone, and collector mineral; attractive druzy surfaces may be set in jewelry. It has limited industrial value compared with bulk quartz.
Geological facts
Botryoidal means grape-like growth; the sparkling surface is druzy quartz rather than metallic glitter. Gray color can result from inclusions, microscopic pores, or trace minerals.
Field identification & locations
Identify by its very fine, rounded chalcedony masses, glassy sparkles, quartz hardness, and lack of obvious cleavage; common sources include Brazil, Uruguay, Mexico, Morocco, and the western United States. Acid does not readily react with it, unlike calcite.
