sedimentary
Chert / Microcrystalline Quartz
Silicon Dioxide (SiO2)
Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- typically tan, gray, or brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: typically tan, gray, or brown; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. Common in limestone and chalk beds.
Uses & applications
Historically used for stone tools and arrowheads; currently used in construction aggregate and as a decorative stone in landscaping.
Geological facts
Because it breaks with a conchoidal fracture like glass, it creates very sharp edges, making it the primary material for prehistoric tools and weapons.
Field identification & locations
Identify by its waxy luster, hardness (will scratch glass), and shark-like shell-shaped fracture patterns. It is one of the most common rocks found in riverbeds and gravel pits.
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