igneous

Granite

Granite (Felsic Plutonic Rock / SiO2 + Al2O3 + K2O + Na2O + CaO + FeO + MgO)

Hardness: 6-7 on Mohs scale. Color: Grayish-white with dark flecks. Luster: Vitreous to dull. Crystal structure: Phaneritic (medium-to-coarse grained) holocrystalline. Cleavage: Indistinct. Specific gravity: 2.63 to 2.75.

Hardness: 6-7 on Mohs scale
Color: Grayish-white with dark flecks
Luster: Vitreous to dull

Identified March 18, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of silica-rich magma deep underground (plutonic). Found in continental crust across all geological ages, notably in Orogenic belts. Most specimens are hundreds of millions to billions of years old.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and curbs. Crushed granite is used as aggregate in road building and concrete. Also used for monuments and cemeteries.

Geological facts

Granite is the most common igneous rock found on Earth's continents. It contains radioactive elements like thorium and uranium, which can decay into radon gas. Mount Rushmore is carved into a massive granite batholith in the Black Hills.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' appearance and visible interlocking mineral crystals (quartz, feldspar, and biotite mica). Found worldwide in mountain ranges. Collectors look for unique color variants like 'pink granite' or large 'pegmatite' crystals.

Other igneous specimens

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Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

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)

mineral

Blue Apatite

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

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral