igneous
Tumbled granite (likely black granite)
Granite; predominantly quartz (SiO₂), feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse, interlocking crystalline texture with black, white, and pink-brown grains; typically Mohs 6–7, vitreous to dull luster, no regular cleavage as a whole, and specific gravity about 2.6–2.8.
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Physical properties
Coarse, interlocking crystalline texture with black, white, and pink-brown grains; typically Mohs 6–7, vitreous to dull luster, no regular cleavage as a whole, and specific gravity about 2.6–2.8.
Formation & geological history
An intrusive igneous rock crystallized slowly from silica-rich magma deep in Earth’s crust, generally during Precambrian or younger continental plutonic events; this piece has been rounded by tumbling.
Uses & applications
Used for countertops, monuments, building stone, aggregate, landscaping, and inexpensive decorative specimens; generally low jewelry value.
Geological facts
The dark grains are commonly biotite or amphibole, while light grains are feldspar and quartz; the visible grain size indicates slow underground cooling.
Field identification & locations
Identify it by its speckled, interlocking grains and inability to scratch glass easily; common worldwide, especially in continental shields and mountain plutons.
