igneous

Diorite

Diorite (intermediate intrusive igneous rock)

Hardness: 6-7 on Mohs scale; Color: Black and white ('salt and pepper' appearance) or greyish-green; Luster: Phaneritic (visible crystals), dull to sub-vitreous; Structure: Coarse-grained crystalline; Cleavage: Two directions at 120 degrees (amphibole) and 90 degrees (plagioclase); Specific Gravity: 2.8-3.0.

Hardness: 6-7 on Mohs scale
Luster: Phaneritic (visible crystals), dull to sub-vitreous

Identified April 7, 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 at subduction zones. It represents a chemical intermediate between felsic granite and mafic gabbro. Typically associated with mountain building events throughout geological history from the Precambrian to Cenozoic.

Uses & applications

Used primarily as a crushed stone for road construction, drainage, and concrete base. High-quality specimens are polished for use as 'black granite' in countertops, building veneers, floor tiles, and cemetery monuments. Historically used by Ancient Egyptians and Mayans for sculpture and masonry due to its durability.

Geological facts

Diorite was the medium used for the famous Code of Hammurabi stele. It is often referred to as 'salt and pepper rock' because of the contrast between light plagioclase feldspar and dark minerals like hornblende or biotite.

Field identification & locations

Identify in the field by its coarse-grained texture and balanced speckled appearance. Unlike granite, it contains little to no visible quartz. It is commonly found in the roots of mountain ranges (plutons) or along plate boundaries. For collectors, look for distinct grain boundaries and lack of layering (foliation).

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