igneous

Diorite

Diorite (Intermediate plutonic rock)

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey/white/black/green); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0

Hardness: 6-7 (Mohs scale)
Color: Salt and pepper (mottled grey/white/black/green)
Luster: Sub-vitreous to dull

Identified April 10, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Salt and pepper (mottled grey/white/black/green); Luster: Sub-vitreous to dull; Structure: Phaneritic (coarse-grained); Specific Gravity: 2.8-3.0

Formation & geological history

Formed from the slow cooling of magma deep underground, typically above subduction zones at convergent plate boundaries. Most specimens range from Proterozoic to Cenozoic in age.

Uses & applications

Used primarily as a decorative stone in construction (curating, flooring), crushed stone for road bases, and historically for sculptures and tools (it is harder than granite).

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 black diorite stele.

Field identification & locations

Identify in the field by its 'salt and pepper' appearance and lack of visible quartz (unlike granite). Commonly found in volcanic arcs and mountain roots such as the Andes, Alps, and Cascades.

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