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 .