igneous

Diorite (Salt and Pepper Rock)

Diorite

Hardness: 6–7 on Mohs scale. Color: Phaneritic (coarse-grained) texture with a speckled 'salt and pepper' appearance of white plagioclase feldspar and black/dark green hornblende or biotite. Luster: Dull to sub-vitreous. Crystal structure: Massive, phaneritic igneous.…

Hardness: 6–7 on Mohs scale
Luster: Dull to sub-vitreous

Identified March 29, 2026More igneous →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed through the slow cooling of magma beneath the Earth's surface (intrusive) in volcanic arcs and mountain-building zones (orogenic belts). It is often associated with subduction zones. Its age varies by location but it has been forming throughout Earth's geological history.

Uses & applications

Extensively used in construction as crushed stone for roads and drainage. In polished form, it is used for countertops, floor tiles, and grave markers (often sold as 'black granite'). Historically used by ancient civilizations like the Egyptians for statues due to its extreme durability.

Geological facts

The famous Code of Hammurabi was inscribed on a massive black diorite stele. Because it is extremely hard, it was difficult for ancient sculptors to work with, making diorite statues a symbol of status and permanence.

Field identification & locations

Identify in the field by its coarse, equal-sized black and white crystals without the presence of visible quartz (unlike granite). Look for it in mountainous regions or volcanic island arcs. Collectors look for 'dalmatian' patterns or specimens with large, distinct crystals.

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