3 FLINT GENUS. 5. Sometimes the edges of the common bafis of the o&aedron are truncated, and, in fome varieties, fo deeply, that a reftangular four* fided ptifm, acuminated by four planes, is formed *. 6. Sometimes all the edges of the odaedron are truncated. When thefe truncations become fo large as to caufe the original faces to dis appear, the garnet dodecaedron is formed. 7: Sometimes each of the angles of the o&ae- dron are acuminated by four planes, which are placed on the lateral planes t- 3. Six-fided table, in which the terminal planes are fet alternately ftraight and oblique on the lateral planes^ It may alfo be viewed as an o&aedron, in which two diagonally oppofite planes have increafed very much in proportion to the others. 9 . When two fegments of the tetraedron are join ed by their bafis, a twin cryftal, having three re-entring angles, is formed. 10. When three fegments are joined, a triple cryftal is formed J. * This variety was firfl dcfcribed by Count de Bournon, and, is far as I recolleft, does not exift in the cabinet of Werner, f This is defcribed by Bournon as a variety*of ceylanite. t Befides the cryftals above enumerated, Werner mentions th e following as belonging to this fpecies: 1. Six-fided prifm, having its alternate and alternating angles truncated. 2. Cube trun cated on the two diagonally oppofite angles. It would a PP fa ^’ however, from the obfervations of Bournon, that thefe varied rather belong to the oriental ruby.
