sedimentary
Chert (Jasper/Flint variety)
Microcrystalline Quartz (SiO2)
Hardness: 6.5-7 (Mohs scale); Color: Olive green, brown, tan; Luster: Waxy to vitreous when wet; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
- Hardness
- 6
- Color
- Olive green, brown, tan
- Luster
- Waxy to vitreous when wet
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Physical properties
Hardness: 6.5-7 (Mohs scale); Color: Olive green, brown, tan; Luster: Waxy to vitreous when wet; Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from groundwater within sedimentary beds. It can be found in formations ranging from Precambrian to Cenozoic ages.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) due to its sharp edges; modern uses include lapidary work, jewelry (especially as jasper), and as an abrasive or construction aggregate.
Geological facts
Because of its conchoidal fracture, chert breaks into edges thinner than a steel scalpel. It is often referred to as 'flint' when found in chalk and 'jasper' when found in colorful, opaque forms.
Field identification & locations
Identify in the field by its hardness (it will scratch glass/steel) and its distinctive smooth, curved 'shell-like' fracture pattern. Common in river beds, beaches, and limestone outcrops.
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