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

Identified May 21, 2026More igneous →

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Physical properties

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.

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Fluorapatite (Ca5(PO4)3F)

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Dark Igneous Rock (Likely Basalt or Diabase)

Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.

Igneous

Magnetite

Iron(II,III) oxide (Fe3O4)

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

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Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

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Magnetite

Magnetite (Fe3O4)

mineral