igneous
Granite Water-Worn Pebble
Felsic intrusive igneous rock (Granite)
Hardness: 6-7 Mohs; Color: Pink, white, and smoky grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Cleavage: Indistinct in hand specimen.
- Hardness
- 6-7 Mohs
- Color
- Pink, white, and smoky grey/black
- Luster
- Dull to vitreous
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Physical properties
Hardness: 6-7 Mohs; Color: Pink, white, and smoky grey/black; Luster: Dull to vitreous; Crystal structure: Phaneritic (visible crystals of quartz, feldspar, and mica); Cleavage: Indistinct in hand specimen.
Formation & geological history
Formed by the slow cooling of silica-rich magma deep underground. This specific specimen has been rounded and smoothed by water erosion in a river or beach environment. Ages vary from Precambrian to Cenozoic.
Uses & applications
Large-scale use in construction (countertops, monuments), aggregate for roads. Smaller pebbles like this are used in decorative landscaping, aquariums, and rock tumbling.
Geological facts
Granite makes up much of the Earth's continental crust. The pink color in this specimen is specifically due to the presence of Potassium Feldspar (Orthoclase).
Field identification & locations
Identify by the 'salt and pepper' appearance and visible interlocking crystals of different colors. It is harder than steel and will not be scratched by a knife. Commonly found in mountainous regions or glacial till.
