Elementary silicon and carborundum

We have mentioned in the previous chapter the two crystalline forms of carbon diamond and graphite. The latter structure is unique among the elements, but a number of other elements of Group IV crystallize with the diamond structure ilicon, germanium, and tin (grey modification). In the B subgroup only lead has a typical metallic structure (cubic close-packed), whereas all the elements of the A subgroup crystallize with close-packed structures. In elementary silicon Si-Si = 2-35 A. 

Carborundum, SiC crystallizes in a large number of forms. The cubic form (/3-SiC) has the zinc-blende structure (p. 102), and in addition there are numerous crystalline modifications all with structures closely related to the zinc-blende and wurtzite structures, which are collectively referred to as a-SiC. The atomic positions 

The geometrical relationship between the structures of zinc-blende, wurtzite, and 

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