igneous
Tumbled larvikite (likely)
Larvikite—alkali feldspar–rich monzonitic rock, commonly containing anorthoclase and dark pyroxene/amphibole
AI-generated identification · may be incorrectDark gray to black, coarse-grained, with silvery-blue feldspar flashes and a vitreous to submetallic polished luster; hardness about 6–6.5 Mohs, no consistent cleavage as a rock, and specific gravity roughly 2.7–2.9.
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Physical properties
Dark gray to black, coarse-grained, with silvery-blue feldspar flashes and a vitreous to submetallic polished luster; hardness about 6–6.5 Mohs, no consistent cleavage as a rock, and specific gravity roughly 2.7–2.9.
Formation & geological history
A slowly cooled intrusive igneous rock formed in the Permian Oslo Rift of southeastern Norway, approximately 290–280 million years ago. The distinctive sheen results from light scattering in intergrown feldspar crystals.
Uses & applications
Used as decorative dimension stone, countertops, monuments, and polished cabochons or tumbled specimens. Small pieces generally have modest collector value.
Geological facts
These pieces appear tumbled or roughly polished; the gray-black color and reflective feldspar pattern are characteristic of larvikite, though similar specimens may be gabbro or labradorite-bearing rock.
Field identification & locations
Identify it by its dense dark body, coarse crystalline texture, and blue-gray feldspar flashes; Norway is the classic source, especially around Larvik. A close photograph and streak, hardness, and mineral examination would be needed for certainty.
