igneous
Demitasse Granite (Diorite-Granite transition)
Intermediate Plutonic Rock (Granodiorite/Diorite mix)
Hardness: 6-7 Mohs; Color: Mottled black, olive-green, and off-white; Luster: Vitreous to dull when wet; Structure: Phaneritic (visible crystals); Cleavage: Perfect in feldspar laths; Specific Gravity: 2.7-3.0
- Hardness
- 6-7 Mohs
- Color
- Mottled black, olive-green, and off-white
- Luster
- Vitreous to dull when wet
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Mottled black, olive-green, and off-white; Luster: Vitreous to dull when wet; Structure: Phaneritic (visible crystals); Cleavage: Perfect in feldspar laths; Specific Gravity: 2.7-3.0
Formation & geological history
Formed through the slow cooling of magma beneath the Earth's surface (intrusive). The dark minerals are likely amphibole or pyroxene, while the lighter green/tan is plagioclase feldspar. Common in continental crust and mountain ranges.
Uses & applications
Used primarily as crushed stone for construction, decorative gravel, and occasionally as architectural stone in larger slabs.
Geological facts
Rocks with this 'salt and pepper' appearance often represent a 'frozen' state of magma mixing. The green tint suggests mild hydrothermal alteration of the mafic minerals into chlorite or epidote group minerals.
Field identification & locations
Identify in the field by the interlocking crystalline texture and lack of layering (foliation). Look for it in riverbeds near mountainous or volcanic roots. It will not scratch with a pocket knife.
