Metamorphic and Igneous
Quartzite (river pebble) and Gabbro (crushed rock)
Quartzite (metamorphosed Quartz Sandstone, SiO2) and Gabbro (Plagioclase-Clinopyroxene rock)
Quartzite: Hardness 7 (Mohs), color peach/tan, vitreous/dull luster, no cleavage. Gabbro: Hardness 6-7, dark grey/black mottled, phaneric (coarse) crystal structure, sub-metallic to vitreous luster.
Identified More metamorphic and igneous →
Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Quartzite: Hardness 7 (Mohs), color peach/tan, vitreous/dull luster, no cleavage. Gabbro: Hardness 6-7, dark grey/black mottled, phaneric (coarse) crystal structure, sub-metallic to vitreous luster.
Formation & geological history
Quartzite formed through regional metamorphism of sandstone; the rounded shape indicates stream transport. Gabbro is an intrusive igneous rock formed from slow-cooling mafic magma. Most surface specimens are Precambrian to Cenozoic.
Uses & applications
Quartzite is used in construction, road ballast, and decor. Gabbro is sold as 'black granite' for countertops and dimension stone. These specific small specimens are used for landscaping or aggregate.
Geological facts
Quartzite is so tough that it usually breaks across the quartz grains rather than around them. Gabbro is the chemical equivalent of basalt but cooled deep underground.
Field identification & locations
Identify Quartzite by its ability to scratch glass and its grainy, sugary look. Identify Gabbro by its dark, interlocking crystals. Commonly found in riverbeds (quartzite) and mountain belts or oceanic crust (gabbro).
More like this
Other metamorphic and igneous specimens
Garnetiferous Pegmatite
Pegmatite with Almandine Garnet and Muscovite
igneous
Milky Quartz
Silicon Dioxide (SiO2)
mineral
Quartz
Silicon dioxide (SiO2)
mineral
Milky Quartz with Iron Staining
Silicon Dioxide (SiO2)
mineral
Quartz (Milky Quartz)
Silicon Dioxide (SiO2)
mineral
Milky Quartz with Iron Staining
Quartz (Silicon Dioxide, SiO2)
mineral