sedimentary
Yellow Chert (Gold-colored River Pebble)
Microcrystalline Quartz (SiO2) with Limonite/Goethite staining
Hardness: 7 on Mohs scale; Color: Dull yellow to mustard gold; Luster: Waxy to dull (earthy); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dull yellow to mustard gold
- Luster
- Waxy to dull (earthy)
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Physical properties
Hardness: 7 on Mohs scale; Color: Dull yellow to mustard gold; Luster: Waxy to dull (earthy); Crystal Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65
Formation & geological history
Formed through the precipitation of silica in sedimentary environments or by the replacement of carbonate rocks. This specimen is a 'river cobble,' rounded by water transport over millions of years, likely dating from the Paleozoic to Cenozoic eras.
Uses & applications
Used historically for stone tools and fire-starting (flint); currently used as architectural aggregate, landscaping stone, and occasionally for lapidary work (cabochons).
Geological facts
Yellow chert gets its distinctive color from iron oxide impurities (Limonite). It is one of the most durable rocks, often surviving long-distance river transport that destroys softer minerals.
Field identification & locations
Identify in the field by its hardness (it will scratch glass), smooth rounded texture from water wear, and lack of visible grains. It is very common in riverbeds, glacial tills, and desert pavements worldwide.
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