sedimentary
Chert / Quartz Pebble
Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Tan, beige, brownish-pink. Luster: Waxy to dull. Crystal structure: Microcrystalline/cryptocrystalline trigonal. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, beige, brownish-pink
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Tan, beige, brownish-pink. Luster: Waxy to dull. Crystal structure: Microcrystalline/cryptocrystalline trigonal. Cleavage: None (conchoidal fracture). Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of siliceous oozes or chemical precipitation of silica in ocean floor or lake bed deposits. River and beach erosion smooths the specimen into rounded pebbles.
Uses & applications
Historically used for making stone tools, flints for spark generation, and decoratively as polished river stones or novelty shape rocks.
Geological facts
Naturally shaped heart stones or uniquely lobed pebbles are formed by irregular water erosion and differential weathering of micro-cracks in cryptocrystalline quartz.
Field identification & locations
Identified by high hardness (scratches glass), waxy luster, smooth water-worn surface, and conchoidal fracturing. Found abundantly in riverbeds, gravel pits, and coastal shores globally.
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