Igneous

Diorite

Phaneritic Intermediate Plutonic Rock

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

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

Identified February 17, 2026More igneous →

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Physical properties

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

Formation & geological history

Formed by the slow cooling of intermediate-composition magma deep beneath the Earth's surface in intrusive bodies like batholiths or laccoliths. Often found above subduction zones.

Uses & applications

Used primarily in construction as crushed stone or road base. Due to its hardness, it is also polished for use as dimension stone, flooring, and kitchen countertops (often sold as 'black granite').

Geological facts

Diorite was used by ancient civilizations for sculpture and inscriptions because of its extreme hardness; the famous Code of Hammurabi was carved into a black diorite stele.

Field identification & locations

Identify in the field by its distinctive equigranular 'salt and pepper' appearance, lacking the pink potassium feldspar of granite. Common in mountainous regions like the Andes. Collectors look for even grain distribution.

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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