sedimentary
Chert (Field-collected Arrowhead-shaped Fragment)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: light grey to tan, Luster: dull to waxy, Crystal structure: Trigonal (microscopic), Cleavage: none (conchoidal fracture), Specific gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: light grey to tan, Luster: dull to waxy, Crystal structure: Trigonal (microscopic), Cleavage: none (conchoidal fracture), Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. Primarily found within limestone or chalk formations.
Uses & applications
Historically used for making stone tools (lithics) like arrowheads and scrapers due to its sharp edges; currently used for decorative stone in landscaping, jewelry (when colorful/jasper variants), and road base construction.
Geological facts
Chert produces sparks when struck against steel, which made it essential for early fire-starting tools and flintlock firearms. The triangular shape of this specimen is suggestive of an 'expedient tool' or a natural shatter fragment that mimics an arrowhead.
Field identification & locations
Identify in the field by its hardness (will scratch glass), smooth waxy feel, and conchoidal fracture (curved, shell-like breaks). Common in riverbeds and limestone outcrops.
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