mineral
Blue-gray chalcedony (rough agate)
Chalcedony, microcrystalline quartz (SiO₂)
AI-generated identification · may be incorrectLikely hardness 6.5–7 Mohs; blue-gray, translucent to opaque, with a waxy to vitreous luster and no visible cleavage. Its fine quartz crystals are too small to distinguish unaided; the brown patches may be iron-bearing material or host rock.
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Physical properties
Likely hardness 6.5–7 Mohs; blue-gray, translucent to opaque, with a waxy to vitreous luster and no visible cleavage. Its fine quartz crystals are too small to distinguish unaided; the brown patches may be iron-bearing material or host rock.
Formation & geological history
Silica-rich fluids deposited quartz in cavities or fractures, commonly in volcanic rocks; the specimen’s age and exact formation cannot be determined from the image.
Uses & applications
Used for beads, cabochons, carvings, and decorative objects; rough pieces are also collected.
Geological facts
Chalcedony is a broad term for fibrous, microcrystalline quartz; agate is typically banded, though banding may not be visible in a small rough piece.
Field identification & locations
Look for a waxy appearance, translucent edges, and hardness sufficient to scratch glass; common sources include Brazil, Uruguay, India, and the western United States. The image alone cannot confirm the identification.
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