igneous

Granite

Granite (composed primarily of Quartz (SiO2), Alkali Feldspar, and Plagioclase)

Hardness: 6-7 on Mohs scale; Color: Phaneritic texture (salt and pepper appearance) with white/grey quartz, white/pink feldspar, and black biotite/hornblende speckles; Luster: Vitreous to dull; Structure: Massive, granular crystalline; Cleavage: Poor; Specific Gravity: 2.63 - 2.75.

Hardness: 6-7 on Mohs scale
Luster: Vitreous to dull

Identified March 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow crystallization of magma below the Earth's surface (intrusive). The large grain size indicates a cooling process that took millions of years. It can date from the Archean Eon to the Cenozoic Era depending on the specific location.

Uses & applications

Extensively used in construction for countertops, floor tiles, paving stones, and monuments (like Mount Rushmore). Historically used for building many of the world's ancient pyramids and temples. Also used as crushed stone for road base.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Unlike oceanic crust (basalt), granite is less dense, which is why the continents 'float' higher on the mantle. The word comes from the Latin 'granum,' meaning a grain.

Field identification & locations

Identify in the field by its coarse-grained interlocking crystals and lack of foliation (layers). It is found in mountain ranges and continental shields globally, such as the Sierra Nevada (USA) or the Scottish Highlands. For collectors, look for specimens with large, well-defined crystals or unique colors.

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

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Blue Apatite

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

mineral

Magnetite

Magnetite (Fe3O4)

mineral