igneous

Diorite

Intermediate plutonic igneous rock

Hardness: 6-7 on Mohs scale; Color: Black and white (salt and pepper appearance); Luster: Phaneritic (coarse-grained) with vitreous minerals; Crystal Structure: Equigranular; Specific Gravity: 2.8-3.0

Hardness: 6-7 on Mohs scale
Color: Black and white (salt and pepper appearance)
Luster: Phaneritic (coarse-grained) with vitreous minerals

Identified May 9, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silicate magma below the Earth's surface (intrusive) in volcanic arcs and mountain-building regions above subduction zones.

Uses & applications

Used primarily as crushed stone for construction, road base, and as a decorative building stone (often sold as 'black granite') for countertops, paving, and monuments.

Geological facts

The famous Code of Hammurabi was inscribed on a 7-foot tall stele made of black diorite. It is often referred to as 'salt and pepper' rock due to its contrasting mineral colors.

Field identification & locations

Identify in the field by its coarse grain size and roughly equal balance of light (plagioclase feldspar) and dark (hornblende or biotite) minerals. Commonly found in large batholiths along continental margins.

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