igneous
Granitoid (River Pebble)
Granite (primarily Quartz, Feldspar, and Mica)
Hardness: 6-7 on Mohs scale; Color: Tan, cream, and grey mottled; Luster: Dull/matte due to weathering; Crystal Structure: Phaneritic (visible crystals); Cleavage: None in the rock overall; Specific Gravity: Approx 2.65-2.75.
- Hardness
- 6-7 on Mohs scale
- Color
- Tan, cream, and grey mottled
- Luster
- Dull/matte due to weathering
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Tan, cream, and grey mottled; Luster: Dull/matte due to weathering; Crystal Structure: Phaneritic (visible crystals); Cleavage: None in the rock overall; Specific Gravity: Approx 2.65-2.75.
Formation & geological history
Formed by the slow cooling of magma deep beneath the Earth's surface. This specific specimen has been significantly rounded and smoothed by water erosion, likely in a river or coastal environment, over centuries or millennia.
Uses & applications
Larger deposits are used for construction, countertops, and monuments. Small pebbles like this are often used in landscaping or as decorative garden stones.
Geological facts
Granite is one of the most common rocks in the Earth's continental crust. Its rounded shape is a result of 'abrasion,' where the rock hits other rocks in moving water.
Field identification & locations
Identify by looking for a 'salt and pepper' appearance of interlocking crystals. This pebble is found globally in riverbeds and on beaches near granitic mountain ranges.
