igneous

Diorite

Diorite (an intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black/grey and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Specific gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: 'Salt and pepper' (mottled black/grey and white)
Luster: Dull to sub-vitreous

Identified February 24, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (mottled black/grey 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 magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is typically of Proterozoic to Cenozoic age.

Uses & applications

Used primarily as a crushed stone for construction, road base, and drainage. High-quality specimens are polished for use as 'black granite' countertops, floor tiles, and gravestones.

Geological facts

The Code of Hammurabi was famously inscribed upon a seven-foot-tall stele of black diorite. It is often confused with gabbro or granite but is mineralogically intermediate between the two.

Field identification & locations

Identify in the field by its distinctive 'salt and pepper' appearance with crystals large enough to see with the naked eye. Commonly found in the Andes Mountains, Guernsey, and the Italian Alps.

Other igneous specimens

See all

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