mineral
Quartz (Chert / Agate / Chalcedony)
Silicon Dioxide (SiO2)
Mohs hardness 7; color ranges from milky white to brownish/translucent; vitreous to waxy luster; conchoidal fracture; hexagonal microcrystalline crystal system.
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Physical properties
Mohs hardness 7; color ranges from milky white to brownish/translucent; vitreous to waxy luster; conchoidal fracture; hexagonal microcrystalline crystal system.
Formation & geological history
Forms through precipitation of silica-rich fluids in cavities, sedimentary beds, or hydrothermal veins. Common in volcanic and sedimentary environments across all geological ages.
Uses & applications
Used in jewelry, tumbling, lapidary art, and rock collections. Historical use for toolmaking (arrowheads/scrapers).
Geological facts
Microcrystalline quartz varieties like agate and chert have been used by humans for hundreds of thousands of years due to their sharp conchoidal fracture.
Field identification & locations
Identified by its high hardness (scratches glass), waxy to glassy luster, shell-like (conchoidal) fracture, and lack of distinct cleavage. Widely found in river beds, gravel deposits, and volcanic rocks worldwide.
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