igneous

Granite (Dioritic variant)

Granite (Phaneritic Igneous Rock)

Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper (yellowish-white feldspar and black biotite/amphibole). Luster: Dull to vitreous when wet. Crystal structure: Phaneritic (coarse-grained visible crystals). Specific Gravity: 2.6-2.7.

Hardness: 6-7 on Mohs scale
Luster: Dull to vitreous when wet

Identified April 8, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of silica-rich magma deep within the Earth's crust (plutonic). This specimen appears to be water-worn, smoothed by fluvial or coastal transport over thousands of years.

Uses & applications

Commonly used in heavy construction, countertops, monuments, and as crushed stone for road bases. Polished versions are used in high-end interior design.

Geological facts

Granite makes up a large portion of the Earth's continental crust. Because it is so hard and durable, it is often the primary material for mountain ranges like the Sierra Nevada.

Field identification & locations

Identify by its 'salt and pepper' appearance and visible interlocking crystals. It is found globally in continental shields and mountain belts. This specific smooth pebble is likely found in a riverbed or beach near a mountain source.

Other igneous specimens

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Blue Apatite

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)

mineral

Blue Apatite

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

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Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral