metamorphic
Garnet-Bearing Gneiss
Almandine-Garnet Gneiss
Hardness: 6.5-7.5 (garnets) | Color: Grey to brownish-buff with brownish-red inclusions | Luster: Vitreous to dull | Crystal Structure: Porphyroblastic with a foliated gneissic matrix | Cleavage: Indistinct | Specific Gravity: 2.7-4.3
- Hardness
- 6
Identified More metamorphic →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness: 6.5-7.5 (garnets) | Color: Grey to brownish-buff with brownish-red inclusions | Luster: Vitreous to dull | Crystal Structure: Porphyroblastic with a foliated gneissic matrix | Cleavage: Indistinct | Specific Gravity: 2.7-4.3
Formation & geological history
Formed through high-grade regional metamorphism of clay-rich sedimentary rocks (pelites) or felsic igneous rocks under intense heat and pressure, often during mountain-building events (orogenies).
Uses & applications
Garnet-rich gneiss is used as an industrial abrasive (sandblasting, waterjet cutting) and in construction for road base or decorative veneer. High-quality garnets within the rock may be used as gemstones.
Geological facts
Garnets are index minerals used by geologists to determine the temperature and pressure history of the Earth's crust. They are the birthstone for January.
Field identification & locations
Identified in the field by its distinct banded appearance (foliation) and the presence of hard, rounded reddish-brown 'eyes' (garnets). Commonly found in Precambrian crystalline shields such as the Adirondack Mountains or the Canadian Shield.
More like this
