igneous

Diorite

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 on the Mohs scale. Color: Mottled 'salt and pepper' appearance (black and white). Luster: Phaneritic (crystalline). Crystal Structure: Coarse-grained phaneritic texture. Cleavage: Good in two directions via feldspar components. Specific Gravity: 2.8-3.0.

Hardness: 6-7 on the Mohs scale
Color: Mottled 'salt and pepper' appearance (black and white)
Luster: Phaneritic (crystalline)

Identified February 25, 2026More igneous →

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Physical properties

Formation & geological history

Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building zones (subduction zones). It is typically of Phanerozoic age but can be found in older Precambrian shields.

Uses & applications

Commonly used as a base material in construction, crushed stone for roads, and occasionally as a polished 'granite' for countertops and floor tiles. Historically used by ancient civilizations for sculpture and tools due to its extreme hardness.

Geological facts

The Code of Hammurabi, one of the oldest deciphered writings of significant length in the world, was inscribed on a 7-foot tall stele made of polished black diorite. It is often confused with granite but lacks significant quartz content.

Field identification & locations

Identify in the field by its distinctive 'salt and pepper' look where the light (plagioclase feldspar) and dark (hornblende or biotite) minerals are roughly equal. Found in large mountain ranges like the Andes or the Cascades. Collectors look for pieces with large, well-defined amphibole crystals.

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

Blue Apatite

Apatite (Group), Ca5(PO4)3(F,Cl,OH)

mineral

Sodalite

Sodalite - Na8(Al6Si6O24)Cl2

mineral

Magnetite

Magnetite (Fe3O4)

mineral