igneous
Tumbled larvikite (likely)
Larvikite, a monzonitic igneous rock composed mainly of alkali feldspar, plagioclase, and pyroxene
AI-generated identification · may be incorrectDark gray to black, polished, with silvery-blue feldspar flashes and faint gray-green veining; hardness about 6–6.5 Mohs, granular crystal structure, poor cleavage as a rock, and specific gravity roughly 2.7–2.9.
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Physical properties
Dark gray to black, polished, with silvery-blue feldspar flashes and faint gray-green veining; hardness about 6–6.5 Mohs, granular crystal structure, poor cleavage as a rock, and specific gravity roughly 2.7–2.9.
Formation & geological history
Formed by slow cooling of magma deep in the crust, producing coarse feldspar crystals; classic larvikite formed in the Permian Oslo Rift of Norway, approximately 300 million years ago.
Uses & applications
Used as decorative building and countertop stone, monuments, tiles, and polished cabochons or worry stones. It is valued for its attractive feldspar schiller.
Geological facts
Its blue-silver sheen is called aventurescence or labradorescence-like flash, caused by light reflecting from feldspar crystal interfaces. The specimen appears tumbled and highly polished.
Field identification & locations
Look for a dense black-gray stone with rounded shape and silvery flashes that move as it is tilted; it is commonly sold from Norway and rock shops worldwide. Similar stones include labradorite and black granite.
