igneous

Diorite

Hardness: 6-7 on Mohs scale. Color: Salt and pepper (mottled grey, white, and black). Luster: Phaneritic (visible crystals), dull to vitreous. Crystal structure: Medium to coarse-grained. Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: Salt and pepper (mottled grey, white, and black)
Luster: Phaneritic (visible crystals), dull to vitreous

Identified June 4, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of magma beneath the Earth's surface in volcanic arches and mountain-building zones (subduction zones). Likely Mesozoic to Cenozoic era.

Uses & applications

Used in construction as crushed stone, for cemetery markers, floor tiles, and as 'black granite' in high-end countertops. Highly valued in ancient civilizations for sculpture due to its extreme hardness.

Geological facts

Diorite was used in ancient Egypt for carving hard stones. The Code of Hammurabi was inscribed on a massive basalt/diorite stele. It is often confused with Granite or Gabbro.

Field identification & locations

Identify by its 'salt and pepper' appearance with equal-sized light and dark mineral grains. Found in volcanic mountain ranges like the Andes or Cascades. Very common in glacial till and riverbeds.

Other igneous specimens

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Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

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Dalmatian Jasper

Aplite with Arfvedsonite inclusions

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Magnetite

Iron(II,III) oxide (Fe3O4)

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