igneous

Diorite (Salt and Pepper Rock)

Phaneritic Plutonic Diorite (Plagioclase Feldspar + Amphibole/Biotite)

Hardness: 6-7 (Mohs scale); Color: Mottled black and white (salt and pepper); Luster: Sub-vitreous to dull; Crystal Structure: Phaneritic (coarse-grained coarse crystals visible to the eye); Cleavage: Good in two directions (feldspar component); Specific Gravity: 2.8 - 3.0

Hardness: 6-7 (Mohs scale)
Color: Mottled black and white (salt and pepper)
Luster: Sub-vitreous to dull

Identified March 2, 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 from the slow cooling of intermediate magma beneath the Earth's surface in volcanic arcs and subduction zones. Most specimens range from the Proterozoic to Cenozoic eras.

Uses & applications

Used primarily in construction as crushed stone, 'black granite' for countertops, base material for roads, and occasionally in sculpture or as ornamental masonry.

Geological facts

Diorite was used by the Ancient Egyptians for statues because of its extreme hardness; the famous Code of Hammurabi was inscribed on a large black diorite stele.

Field identification & locations

Identify by its distinctive black-and-white speckled appearance and hard, interlocking crystals. Common in mountain ranges like the Andes and the Cascades; collectors should look for smooth, water-worn cobbles in riverbeds near volcanic regions.

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