igneous
Tumbled larvikite (likely)
Larvikite; plagioclase feldspar, commonly with augite and biotite
AI-generated identification · may be incorrectDark gray to blue-black, polished vitreous luster with blue-silver feldspar flashes; hardness about 6–6.5 Mohs, granular crystalline texture, poor cleavage in the whole stone, and specific gravity about 2.65–2.75.
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Physical properties
Dark gray to blue-black, polished vitreous luster with blue-silver feldspar flashes; hardness about 6–6.5 Mohs, granular crystalline texture, poor cleavage in the whole stone, and specific gravity about 2.65–2.75.
Formation & geological history
An alkaline igneous intrusive rock formed by slow cooling of feldspar-rich magma, mainly in the Permian Oslo Rift of southern Norway, roughly 290–250 million years ago.
Uses & applications
Used as decorative and dimension stone, countertops, tiles, monuments, and polished cabochons or worry stones.
Geological facts
Its blue iridescence, called schiller, comes from light scattering in closely intergrown feldspar crystals; it is sometimes marketed as “blue labradorite” or “black moonstone,” though those names can be misleading.
Field identification & locations
Identify it by the dark coarse-grained body and blue flashes that move across the surface when tilted; common sources are Norway and related feldspathic rocks worldwide. The image supports a likely identification, but a close look or hardness/mineral test would confirm it.
