igneous
Diorite (Porphyritic Diorite)
Porphyritic Diorite
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance with white/cream plagioclase feldspar phenocrysts in a dark mafic matrix (biotite, hornblende, pyroxene). Luster: Dull to sub-vitreous. Cleavage: Good in plagioclase grains. Specific Gravity: 2.8 - 3.0.
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Salt-and-pepper appearance with white/cream plagioclase feldspar phenocrysts in a dark mafic matrix (biotite, hornblende, pyroxene). Luster: Dull to sub-vitreous. Cleavage: Good in plagioclase grains. Specific Gravity: 2.8 - 3.0.
Formation & geological history
Formed by the slow cooling of intermediate, silica-medium magma beneath the Earth's surface in subduction zones and volcanic arcs. Porphyritic texture indicates a two-stage cooling history: early slow cooling formed larger phenocrysts followed by faster cooling.
Uses & applications
Used as crushed stone for road construction, dimension stone for buildings and monuments, decorative polished landscaping stones, and lapidary tumbling.
Geological facts
Diorite is so durable that ancient civilizations, including the Akkadians, Egyptians, and Maya, used it for carving statues and inscriptions, such as the famous Code of Hammurabi carved on a diorite stele.
Field identification & locations
Identified in the field by its distinctive coarse-grained, high-contrast black-and-white 'dalmatian' or 'snowflake' pattern without significant quartz. Commonly found in subduction zones, continental volcanic arcs, and batholiths worldwide.
