igneous

Granite

Granite (Felsic Plutonic Rock)

Hardness: 6-7 on Mohs scale. Color: can range from white/gray to pink/tan with black specks. Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained visible crystals). Cleavage: Varies by mineral constituent (feldspar has 2 planes, quartz has none). Specific Gravity: 2.63 - 2.75.

Hardness: 6-7 on Mohs scale
Color: can range from white/gray to pink/tan with black specks
Luster: Vitreous to dull

Identified March 23, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below the Earth's surface (intrusive). Most granites date from the Precambrian to Cenozoic eras, typically found in continental crust and mountain ranges.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, curbing, and monuments. Also used as crushed stone for road base and railroad ballast.

Geological facts

Granite is the most common igneous rock found on the Earth's surface. Mount Rushmore is carved into a granite batholith, and it is a primary component of the continental crust.

Field identification & locations

Identify by its interlocking 'salt and pepper' appearance of quartz (clear/gray), feldspar (white/pink), and mica (black/shiny). Found in terminal moraines, mountain cores, and outcrops. Collectors look for unique large-crystal varieties (pegmatites).

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