An archaic or variant plural form of basalt, a dark volcanic rock formed from cooled lava.
From Greek 'basanites' (touchstone), named for a dark stone used to test the purity of gold and silver. The -es is a classical Greek plural ending that persisted in early English scientific texts.
The ancient Greeks called this rock 'basanites' because they used it literally as a 'test stone'—by rubbing precious metals against it, they could tell if the gold was real or fake!
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