igneous
Diorite (Porphyritic) / Granite
Plutonic Igneous Rock (Granodiorite / Diorite)
Hardness: 6-7 on Mohs scale. Color: Tan-brown weathered matrix with dark black/dark green amphibole or biotite phenocrysts. Luster: Dull to earthy (weathered), vitreous on fresh mineral surfaces. Texture: Phaneritic to porphyritic with visible interlocking mineral grains.
- Hardness
- 6-7 on Mohs scale
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Physical properties
Hardness: 6-7 on Mohs scale. Color: Tan-brown weathered matrix with dark black/dark green amphibole or biotite phenocrysts. Luster: Dull to earthy (weathered), vitreous on fresh mineral surfaces. Texture: Phaneritic to porphyritic with visible interlocking mineral grains.
Formation & geological history
Formed deep underground through the slow cooling and crystallization of intermediate to felsic magma. Weathering gives the outer surface a yellowish-brown iron oxide patina, while dark mafic minerals (hornblende/biotite) remain visible as spots.
Uses & applications
Used as crushed stone in construction, road base, and as decorative gravel. Unweathered granite/diorite is widely used for dimension stone, countertops, and monuments.
Geological facts
Diorite is often nicknamed 'Dalmatian stone' or 'leopard stone' when it features dark, spotted mineral inclusions in a light-colored matrix. Porphyritic igneous rocks reflect two stages of cooling: slow cooling deep underground followed by faster cooling higher up.
Field identification & locations
Identified by its salt-and-pepper or spotted appearance with interlocking visible crystals. Common in continental crust and mountain-building regions globally, often found as stream-rounded river pebbles or eroded glaciated cobbles.
