1911 Encyclopædia Britannica/Bort

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BORT,or Boart, an inferior kind of diamond, unfit for cutting but useful as an abrasive agent. The typical bort occurs in small spherical masses, of greyish colour, rough or drusy on the surface, and showing on fracture a radiate crystalline structure. These masses, known in Brazil as bolas, are often called “shot bort” or “round bort.” Much of the bort consists of irregular aggregates of imperfect crystals. In trade, the term bort is extended to all small and impure diamonds, and crystalline fragments of diamond, useless as gem-stones. A large proportion of the output of some of the South African mines consists of such material. This bort is crushed in steel mortars to form diamond powder, which is largely used in lapidaries' work.