igneous

Diorite

Phaneritic Intrusive Igneous Rock (composed of Plagioclase feldspar, Hornblende, and Biotite)

Hardness (Mohs): 6-7; Color: Black and white 'salt and pepper' appearance; Luster: Sub-vitreous to dull; Crystal Structure: Phaneritic (coarse-grained, visible crystals); Specific Gravity: 2.8 - 3.0. It lacks the pinkish potassium feldspar and high quartz content of granite.

Color: Black and white 'salt and pepper' appearance
Luster: Sub-vitreous to dull

Identified March 7, 2026More igneous →

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Physical properties

Formation & geological history

Formed through the slow cooling of magma beneath the Earth's surface in volcanic arcs and mountain-building regions above subduction zones. Typically formed during major orogenic events throughout geological history, often found in major batholiths.

Uses & applications

Widely used as 'crushed stone' for road construction and parking lots. When polished, it is used as dimension stone for building facades, floor tiles, and more rarely as polished river stones or garden ornaments.

Geological facts

Diorite was extremely popular in Ancient Egypt for sculpting, as it is harder than stone-age tools. The famous Code of Hammurabi was inscribed on a massive stele made of a variety of black diorite.

Field identification & locations

Identify in the field by its speckled 'salt and pepper' texture; unlike granite, it contains little to no visible quartz and is darker. Found worldwide in regions with past volcanic activity like the Andes Mountains, the Alps, and the Appalachian range. For collectors, rounded river-worn specimens like this are common.

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