igneous

Diorite

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 Mohs; Color: Salt-and-pepper (speckled black and white/grey); Luster: Dull to sub-vitreous; Crystal structure: Phaneritic (coarse-grained visible crystals); Cleavage: Distinct in feldspars; Specific gravity: 2.8-3.0.

Hardness: 6-7 Mohs
Color: Salt-and-pepper (speckled black and white/grey)
Luster: Dull to sub-vitreous

Identified January 13, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of intermediate-silica magma deep beneath the Earth's surface in subduction zones or volcanic arcs. It primarily dates from Various geological eras depending on tectonic local history.

Uses & applications

Used as a base material in construction, crushed stone for road building, and as a decorative building stone. Historically used for sculpture and monuments (e.g., Code of Hammurabi) due to its extreme durability.

Geological facts

Diorite is often called 'Black Granite' in the commercial stone trade, but geologically it contains little to no quartz compared to true granite. The Code of Hammurabi, one of the oldest deciphered writings in history, was carved into a diorite stele.

Field identification & locations

Identify in the field by its characteristic 'salt and pepper' appearance and visible interlocking crystals of white plagioclase feldspar and dark hornblende/biotite. Found in batholiths and mountain roots in areas like the Andes, the Cascades, and parts of the UK.

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