igneous

Diorite

Intrusive Igneous Diorite

Phaneritic (coarse-grained) texture, salt and pepper appearance, hardness 6-7 on Mohs scale, white to gray plagioclase feldspar and black hornblende or biotite, dull to vitreous luster, specific gravity 2.8-3.0.

Identified May 30, 2026More igneous →

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Physical properties

Formation & geological history

Formed by the slow cooling of silicate magma below the Earth's surface in volcanic arcs and mountain-building regions. It often forms part of larger batholiths or as smaller dikes and sills.

Uses & applications

Used in construction as crushed stone for roads and drainage, as dimension stone for architectural facades, countertops, and floor tiles. Historically used in sculpting (e.g., Code of Hammurabi).

Geological facts

Diorite is often called 'Salt and Pepper stone' due to its distinct black and white speckled look. It was one of the few stones hard enough for the Ancient Egyptians and Mesopotamians to use for durable statues and steles.

Field identification & locations

Identify in the field by its phaneritic texture with approximately equal parts light and dark minerals, lack of visible quartz (unlike granite), and its extreme toughness. Commonly found in subduction zones like the Andes or the Cascade Mountains.

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