Igneous
Granite (with mafic xenolith)
Phaneritic Felsic Plutonic Rock
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white/grey with black spots); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarsegrained visible crystals); Cleavage: Distinct in feldspar grains; Specific gravity: 2.63 - 2.75
- Hardness
- 6-7 Mohs
- Color
- Salt-and-pepper (white/grey with black spots)
- Luster
- Vitreous to dull
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Physical properties
Hardness: 6-7 Mohs; Color: Salt-and-pepper (white/grey with black spots); Luster: Vitreous to dull; Crystal structure: Phaneritic (coarsegrained visible crystals); Cleavage: Distinct in feldspar grains; Specific gravity: 2.63 - 2.75
Formation & geological history
Formed from the slow cooling of silica-rich magma deep underground (plutonic). The dark patch is likely a xenolith—a piece of pre-existing country rock or earlier-crystallized mafic magma that was trapped in the granite as it cooled. Aged from Precambrian to Cenozoic depending on location.
Uses & applications
Used extensively in construction for countertops, floor tiles, paving stones, and memorial monuments. It is also an important source of aggregate for road building.
Geological facts
Granite makes up a significant portion of the Earth's continental crust. The dark inclusion seen in this specimen is known as a 'mafic enclave' or 'xenolith', representing a moment of magma mixing or crustal assimilation.
Field identification & locations
Identify by its interlocking 'salt and pepper' crystalline texture and extreme hardness. It won't be scratched by a steel knife. Commonly found in mountainous regions or where ancient shields are exposed at the surface.
