igneous

Diorite

Diorite (Intermediate Plutonic Rock)

Hardness: 6-7 Mohs; Color: Salt and pepper (black and white); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8 - 3.0

Hardness: 6-7 Mohs
Color: Salt and pepper (black and white)
Luster: Dull to sub-vitreous

Identified May 3, 2026More igneous →

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Physical properties

Hardness: 6-7 Mohs; Color: Salt and pepper (black and white); Luster: Dull to sub-vitreous; Crystal Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8 - 3.0

Formation & geological history

Formed by the slow cooling of silicate magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It consists mainly of plagioclase feldspar and hornblende/biotite.

Uses & applications

Used primarily as crushed stone for road construction and as a decorative building stone known as 'black granite'. Historically used for sculptures and inscriptions, such as the Code of Hammurabi.

Geological facts

The famous Code of Hammurabi was inscribed on a 7-foot tall stele of black diorite. It is often confused with granite but lacks significant quartz.

Field identification & locations

Identify by its 'salt and pepper' appearance and lack of visible quartz crystals. Found in locations like the Andes Mountains, Italy, and various parts of North America.

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