igneous
Diorite Porphyry (Polished Pebble)
Diorite
Hardness: 6-7 Mohs; Color: White or light grey base with dark black/grey mineral spots; Luster: Dull to sub-vitreous when polished; Crystal structure: Phaneritic (medium-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- White or light grey base with dark black/grey mineral spots
- Luster
- Dull to sub-vitreous when polished
Identified More igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6-7 Mohs; Color: White or light grey base with dark black/grey mineral spots; Luster: Dull to sub-vitreous when polished; Crystal structure: Phaneritic (medium-grained); Specific Gravity: 2.8-3.0
Formation & geological history
Formed by the slow cooling of magma beneath the Earth's surface (intrusive), typically in volcanic arc environments above subduction zones. It represents a composition intermediate between felsic granite and mafic gabbro.
Uses & applications
Used in construction as crushed stone, for floor tiles, paving stones, and as decorative semi-precious gemstones/polished pocket stones. Historically used for carving, notable for being the medium of the Code of Hammurabi.
Geological facts
Diorite is often called 'Black and White Granite' in the commercial stone trade, though it lacks the high quartz content required to be true granite. Porphyritic diorite features distinctively larger crystals (phenocrysts) set in a finer matrix.
Field identification & locations
Identified by its 'salt and pepper' appearance. Look for a mix of light plagioclase feldspar and dark amphibole (hornblende) or biotite. It is extremely durable and resistant to weathering.
