sedimentary
Chert with Quartz Druzy
Microcrystalline Quartz (SiO2) with Drusy Quartz Coating
Hardness: 7 (Mohs scale), Color: White, tan, and reddish-brown, Luster: Vitreous to waxy, Crystal structure: Hexagonal/Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
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Physical properties
Hardness: 7 (Mohs scale), Color: White, tan, and reddish-brown, Luster: Vitreous to waxy, Crystal structure: Hexagonal/Trigonal, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7
Formation & geological history
Formed through the accumulation of silica-rich organic remains or chemical precipitation in sedimentary environments. The white crystalline coating formed as secondary silica-rich fluids crystallized as small quartz points (druzy) on the surface over millions of years.
Uses & applications
Used historically for stone tools due to its sharp conchoidal fracture. Modern uses include architectural decorative stone, road filler in aggregate, and as mineral specimens for collectors.
Geological facts
Chert and its variety flint were some of the most important minerals for early human civilization, providing the sharp edges needed for survival. Druzy coatings occur when mineral-rich water evaporates or cools slowly on a rock surface.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), its shell-like conchoidal fracture edges, and the presence of tiny sparkling crystals. Commonly found in limestone and chalk beds worldwide.
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