igneous

Diorite

Diorite (intermediate intrusive igneous rock)

Hardness: 6-7 Mohs. Color: Salt-and-pepper (speckled black and white). Luster: Dull to sub-vitreous. Structure: Phaneritic (coarse-grained). Composition: Primarily plagioclase feldspar, hornblende, and biotite. Specific Gravity: 2.8-3.0.

Hardness: 6-7 Mohs
Color: Salt-and-pepper (speckled black and white)
Luster: Dull to sub-vitreous

Identified March 27, 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 and mountain-building zones (subduction zones). It is typically intrusive and often occurs as large plutons or batholiths.

Uses & applications

Used primarily as crushed stone for road construction and drainage. It can be polished as 'black granite' for countertops, flooring, and decorative building stone. Historically used by ancient civilizations for sculpture due to its durability.

Geological facts

The famous Code of Hammurabi was inscribed on a large diorite stele over 7 feet tall. It is often confused with gabbro or granite, but contains more feldspar than gabbro and less quartz than granite.

Field identification & locations

Identify in the field by its distinctive 'salt-and-pepper' speckled appearance with visible interlocking crystals. Common in the Andes Mountains of South America and various mountain ranges in North America. Collectors look for large, well-defined hornblende crystals.

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

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