igneous

Diorite

Intermediate Phaneritic Igneous Rock

Hardness: 6-7 on Mohs scale; Color: 'Salt and pepper' (black and white/gray); Luster: Sub-vitreous to dull; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in two directions for amphibole/feldspar components; Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: 'Salt and pepper' (black and white/gray)
Luster: Sub-vitreous to dull

Identified June 2, 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 arcs or above subduction zones. It has an intermediate chemical composition between granite and gabbro and typically dates from various periods of tectonic activity throughout Earth's history.

Uses & applications

Used as a crushed stone for road construction, as a building stone for facades (often marketed as 'black granite'), and historically for tools and monumental sculptures due to its extreme hardness.

Geological facts

The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a 7-foot tall diorite stele. It is harder than granite and was favored by ancient Egyptian and Mesopotamian sculptors.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' appearance with roughly equal parts dark (hornblende/biotite) and light (plagioclase feldspar) minerals. Commonly found in large mountain ranges such as the Andes.

Other igneous specimens

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Granite

Igneous

Granite

Igneous

Blue Apatite

Fluorapatite (Ca5(PO4)3F)

mineral

Dalmatian Jasper

Aplite with Arfvedsonite inclusions

igneous

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