igneous

Diorite

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale. Color: 'Salt and pepper' (mottled black and white). Luster: Phaneritic (crystalline, dull to sub-glassy). Crystal structure: Coarse-grained equigranular. Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Color: 'Salt and pepper' (mottled black and white)
Luster: Phaneritic (crystalline, dull to sub-glassy)

Identified April 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of silicate magma below the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is usually Mesozoic to Cenozoic in age but can be found in older cratons.

Uses & applications

Used primarily as crushed stone for road construction and aggregate. High-quality specimens are polished and used as 'black granite' for countertops, floor tiles, and ornamental building veneers.

Geological facts

Diorite was used in ancient Egypt and Mesopotamia for sculptures and tablets because of its extreme hardness; the famous Code of Hammurabi is inscribed on a diorite stele.

Field identification & locations

Identify by its coarse-grained texture and near-equal mix of dark (amphibole/biotite) and light (plagioclase feldspar) minerals. Found in large mountain ranges like the Andes or the 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

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