igneous

Diorite

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 (Mohs scale); Color: Mottled 'salt and pepper' appearance (black and white); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained); Cleavage: Distinct in feldspar components; Specific gravity: 2.8 - 3.0

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

Identified April 12, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones above subduction zones. Typically Mesozoic to Cenozoic in age depending on location.

Uses & applications

Used primarily in construction as crushed stone or road base. In its more attractive forms, it is used as dimension stone for building facades, floor tiles, and countertops (often sold as 'black granite').

Geological facts

Diorite was used in ancient Egypt and Mesopotamia because of its extreme hardness; the famous Code of Hammurabi is inscribed on a diorite stele. It is often referred to as 'salt and pepper' rock due to the balanced mix of light and dark minerals.

Field identification & locations

Identify in the field by its phaneritic texture containing roughly equal parts light plagioclase feldspar and dark minerals like hornblende or biotite. It lacks the visible quartz typical of granite. Common in the Andes Mountains and the cascades of North America.

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

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