metamorphic and sedimentary
Quartzite and Chert
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale), Color: tan, reddish-brown, and cream. Luster: vitreous to waxy. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture).
- Hardness
- 7 (Mohs scale), Color: tan, reddish-brown, and cream
- Color
- tan, reddish-brown, and cream
- Luster
- vitreous to waxy
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Physical properties
Hardness: 7 (Mohs scale), Color: tan, reddish-brown, and cream. Luster: vitreous to waxy. Crystal structure: Trigonal (microcrystalline). Cleavage: None (conchoidal fracture).
Formation & geological history
Quartzite forms from the metamorphism of quartz sandstone under heat and pressure. Chert forms through the accumulation of silica-rich organic remains or chemical precipitation in marine environments. These specimens appear water-worn or tumbled.
Uses & applications
Used as lapidary material for jewelry, beads, and stone tools historically. In modern times, they are often used as decorative landscaping stones or aquarium pebbles.
Geological facts
Chert was one of the first materials used by early humans to create arrowheads and scrapers due to its sharp conchoidal fracture. Quartzite is one of the most durable and weather-resistant rocks on Earth.
Field identification & locations
Identified by high hardness (cannot be scratched by steel) and lack of visible grains in the chert piece. Commonly found along riverbeds, beaches, and in glacial till.
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