igneous

Diorite (with Salt-and-Pepper Texture)

Diorite (Intrusive Igneous Rock)

Hardness: 6-7 (Mohs scale); Color: Mottled black and white ('salt and pepper'); Luster: Phaneritic (crystalline, visible grains); Crystal structure: Coarse-grained/crystalline; Specific Gravity: 2.8-3.0.

Hardness: 6-7 (Mohs scale)
Color: Mottled black and white ('salt and pepper')
Luster: Phaneritic (crystalline, visible grains)

Identified March 29, 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 or massive mountain ranges. It is intermediate in composition between granite and gabbro, often dating back millions of years depending on the regional tectonic history.

Uses & applications

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

Geological facts

Diorite was used by ancient civilizations, such as the Babylonians and Egyptians, for statues and inscriptions because of its extreme hardness; the Code of Hammurabi was famously carved into a diorite stele.

Field identification & locations

Identify in the field by looking for a 'mosaic' of roughly equal parts dark (hornblende/biotite) and light (plagioclase feldspar) minerals. Found in batholiths and mountain-forming regions like the Andes or Cascades.

Other igneous specimens

See all

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