sedimentary
Limonite-stained Chert
Microcrystalline Quartz (SiO2) with Goethite/Limonite (FeO(OH)·nH2O)
Hardness: 7 (Mohs); Color: Tan, brown, and ochre yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7.
- Hardness
- 7 (Mohs)
- Color
- Tan, brown, and ochre yellow
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs); Color: Tan, brown, and ochre yellow; Luster: Waxy to dull; Structure: Cryptocrystalline; Fracture: Conchoidal; Specific Gravity: 2.6-2.7.
Formation & geological history
Formed in marine environments through the accumulation of siliceous remains or chemical replacement of carbonates. The yellow/brown staining is due to secondary iron oxide weathering.
Uses & applications
Historically used for stone tools due to sharp edges; currently used for road ballast, landscaping, and occasionally as lapidary material.
Geological facts
Chert was one of the most important minerals for early humans to create arrowheads and scrapers. The yellow coloration is essentially the same chemical composition as common rust.
Field identification & locations
Identify in the field by its hardness (scratches glass), waxy texture when broken, and lack of visible grains. Common in limestone deposits and riverbeds.
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