There is no distinct cleavage, but imperfect parting may be obtained along octahedral planes.
The octahedral formula discussed by Julius Thomsen (Ber., 1886, 19, p. 2 944) consists of the six carbon atoms placed at the corners of a regular octahedron, and connected together by the full lines as shown in (I); a plane projection gives a hexagon with diagonals (II).
Soc. Trans., p. 1013) considered in detail an octahedral form, and showed how by means of certain simple rotations of his system the formulae of Kekule and Claus could be obtained as projections.
From the alloy containing 25% of silicon, the excess of magnesium is removed by a mixture of ethyl iodide and ether and a residue consisting of slate-blue octahedral crystals of magnesium silicide is left.
BORAX (sodium pyroborate or sodium biborate), Na2B407, a substance which appears in commerce under two forms, namely "common" or prismatic borax, Na 2 B 4 O 7.10H 2 O, and "jewellers'" or octahedral borax, Na 2 B 4 O 7.5H 2 O.