sedimentary

Chert (Iron-stained or Jasperoid)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Yellowish-brown, ochre, or rusty due to iron oxide; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Yellowish-brown, ochre, or rusty due to iron oxide
Luster: Waxy to dull

Identified April 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from hydrothermal fluids in sedimentary environments. Its iron staining often occurs later through groundwater infiltration.

Uses & applications

Historically used for stone tools (knapping) due to its sharp edges; currently used for decorative stone, landscaping, and as a collector's specimen.

Geological facts

Chert and Jasper are often used interchangeably by collectors. When it is red or brownish-orange and opaque, it is frequently called Jasper. It is very chemically stable and highly resistant to weathering.

Field identification & locations

Identify in the field by its hardness (it can scratch glass and steel) and its conchoidal (shell-like) fracture pattern. It is common in limestone formations and riverbeds across North America.

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