igneous
Diorite (Dalmatian Stone)
Diorite (Intermediate Plutonic Rock)
Hardness: 6-7 (Mohs); Color: Mottled white and black or dark gray; Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained); Composition: Plagioclase feldspar, hornblende, and biotite.
- Hardness
- 6-7 (Mohs)
- Color
- Mottled white and black or dark gray
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 (Mohs); Color: Mottled white and black or dark gray; Luster: Dull to sub-vitreous; Structure: Phaneritic (coarse-grained); Composition: Plagioclase feldspar, hornblende, and biotite.
Formation & geological history
Formed from the slow cooling of magma beneath the Earth's surface in volcanic arcs and subduction zones. This specimen is a water-worn river pebble or cobble.
Uses & applications
Used in construction as crushed stone, for architectural facings, and small polished pebbles are often sold in the lapidary trade as decorative stones.
Geological facts
Often called 'salt and pepper' rock due to its speckled appearance. It is chemically intermediate between granite and gabbro. Historically, diorite was used by ancient civilizations like the Egyptians for durable statues and stelae.
Field identification & locations
Identify by its 'salt and pepper' appearance where black and white minerals are roughly equal in size. Commonly found in mountain ranges such as the Andes or the Cascades. Collectors look for high-contrast specimens.
