sedimentary
Chert (River Pebble)
Microcrystalline Quartz (SiO2)
Hardness: 7 Mohs scale; Color: Sage green, grey, and brown bands; Luster: Waxy to dull (glassy when wet); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Sage green, grey, and brown bands
- Luster
- Waxy to dull (glassy when wet)
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Physical properties
Hardness: 7 Mohs scale; Color: Sage green, grey, and brown bands; Luster: Waxy to dull (glassy when wet); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed by the precipitation of silica-rich fluids in marine environments or the accumulation of silica-based skeletal remains of microscopic organisms like diatoms and radiolaria. This specimen looks to be a stream-tumbled pebble, likely from the Paleozoic or Mesozoic era.
Uses & applications
Historically used for making stone tools (arrowheads). Today used as decorative gravel, in lapidary work for cabochons, and as an industrial abrasive.
Geological facts
Chert is essentially the same material as flint, but the term 'flint' is usually reserved for dark varieties found in chalk beds. Green varieties are often called 'green chert' or sometimes 'jasper' if high in iron impurities.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), conchoidal fracture (curved, shell-like breaks), and its smooth, waxy surface. Often found in riverbeds and limestone outcrops.
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