igneous and mineral
Basalt and Quartz pebbles
Basalt (extrusive igneous rock) and Quartz (SiO2)
Hardness: 6-7 Mohs. Colors: Dark grey/black for basalt, white/off-white for quartz. Luster: Dull to waxy. Basalt is fine-grained; Quartz is crystalline and massive.
- Hardness
- 6-7 Mohs
- Luster
- Dull to waxy
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Physical properties
Hardness: 6-7 Mohs. Colors: Dark grey/black for basalt, white/off-white for quartz. Luster: Dull to waxy. Basalt is fine-grained; Quartz is crystalline and massive.
Formation & geological history
The dark stones are basalt formed from cooling lava; the white stone is quartz formed from hydrothermal veins. Both are water-worn and smoothed by river or glacial transport.
Uses & applications
Common river stones used for landscaping, garden decoration, or road base; quartz is used in jewelry and glass manufacturing.
Geological facts
Basalt is the most common rock type in Earth's crust, making up most of the ocean floor. Quartz is the second most abundant mineral in Earth's continental crust.
Field identification & locations
Found commonly in riverbeds and glacial deposits. Identify basalt by its weight and dark, uniform color; identify quartz by its hardness (scratches glass) and whitish translucency.
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