An imperfectly crystallized form of diamond; industrial-grade or poor-quality diamond used for cutting tools and abrasives.
From the name Ballas in Germany, where such diamonds were originally found and processed; also possibly related to 'ballast.' The term entered English in the 19th century as the diamond industry developed.
Ballas diamonds are failed diamonds—they can't be polished into gems, but that 'failure' makes them perfect for grinding and sawing, meaning some of the hardest-working diamonds in industry are the rejects.
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