Igneous

Diorite (Polished Tumble)

Diorite (Intermediate intrusive igneous rock)

Hardness: 6-7 (Mohs scale); Color: Black and white 'salt and pepper' appearance; Luster: Phaneritic (crystalline/glassy when polished); Crystal structure: Coarse-grained; Specific gravity: 2.8-3.0

Hardness: 6-7 (Mohs scale)
Color: Black and white 'salt and pepper' appearance
Luster: Phaneritic (crystalline/glassy when polished)

Identified March 30, 2026More igneous →

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Physical properties

Hardness: 6-7 (Mohs scale); Color: Black and white 'salt and pepper' appearance; Luster: Phaneritic (crystalline/glassy when polished); Crystal structure: Coarse-grained; Specific gravity: 2.8-3.0

Formation & geological history

Formed through the slow cooling of silicate magma below the Earth's surface in volcanic arcs or cordilleras. It typically dates from various geological periods where tectonic convergence occurred, such as the Cenozoic or Mesozoic.

Uses & applications

Used primarily as a construction material (crushed stone, base material) and in decorative architecture. High-quality varieties are used for funeral monuments and kitchen countertops.

Geological facts

Diorite is often called 'Black Granite' in the commercial stone trade. Historically, it was used by ancient civilizations like the Egyptians and Sumerians for statues and stelae, including the Code of Hammurabi.

Field identification & locations

Identify by its interlocking black (amphibole/biotite) and white (plagioclase feldspar) grains. Commonly found in batholiths and mountain roots in the Andes, the Alps, and western North America.

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