igneous
Orbicular gabbro (orbicular norite)
Coarse-grained mafic intrusive rock, chiefly plagioclase feldspar and pyroxene, with dark mafic matrix
AI-generated identification · may be incorrectHardness about 6–7; black to dark gray matrix containing cream-white rounded orbicules and feldspar-rich patches. Granular, crystalline texture with vitreous to dull luster; no consistent cleavage as a whole, though feldspar and pyroxene grains cleave.
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Physical properties
Hardness about 6–7; black to dark gray matrix containing cream-white rounded orbicules and feldspar-rich patches. Granular, crystalline texture with vitreous to dull luster; no consistent cleavage as a whole, though feldspar and pyroxene grains cleave.
Formation & geological history
Formed by slow cooling of mafic magma deep in the crust, with orbicules developing through rhythmic mineral growth around nuclei; commonly Precambrian to Paleozoic in age, depending on locality.
Uses & applications
Used mainly as a decorative and collector stone for polished slabs, cabochons, and display specimens; occasionally used for ornamental facing, but it is uncommon and not a standard construction aggregate.
Geological facts
The rounded, concentric-looking light bodies are orbicules, making this an unusual textural variety rather than ordinary granite or concrete.
Field identification & locations
Identify it by the natural interlocking crystalline texture, very dark pyroxene-rich matrix, and irregular cream feldspar/orbicule inclusions; notable material occurs in Finland and parts of Scandinavia. A fresh surface is typically more diagnostic than a weathered one.
