igneous

Diorite

Diorite (Intermediate plutonic rock)

Hardness: 6-7 on Mohs scale. Color: 'Salt and pepper' (mottled white and black/dark grey). Luster: Vitreous to dull. Crystal structure: Phaneritic (coarse-grained). Cleavage: Imperfect to good based on feldspar content.

Hardness: 6-7 on Mohs scale
Color: 'Salt and pepper' (mottled white and black/dark grey)
Luster: Vitreous to dull

Identified April 11, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of magma deep underground, often in subduction zones above continental plates. It is an intrusive rock that crystallizes at greater depths than andesite.

Uses & applications

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

Geological facts

Diorite was used in ancient Egypt and Mesopotamia for sculptures because it is extremely hard and durable. The famous Code of Hammurabi was inscribed on a black diorite stele.

Field identification & locations

Identify by its distinct medium-to-coarse grain size and lack of visible quartz compared to granite. It contains roughly equal parts light plagioclase feldspar and dark minerals like hornblende or biotite. Commonly found in mountain-building regions (orogenic belts).

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