Mineralogical Magazine and Journal of the Mineralogical Society · 1925 · 21 citations · 2 references
Natural SciencesChemistryMaterials ScienceCrystal StructureMineralogyPhysical ChemistryCrystal ChemistryCrystal LatticeCrystal SymmetryCrystal SystemsCrystallographyMetal SulfidesAxial RatioCleavageCrystal Chemistry Of SulfidesCrystal Structure Of SulfidesCrystal Structures Of Metal SulfidesMercury SulfidesSulfide Crystal StructuresTrigonal System
Mercuric sulphide, HgS, occurs in nature as two well-known modifications, cinnabar and metacinnabarite. The latter is some what rare and occurs as black cubic crystals possessing the symmetry of the zinc-bleude, i.e. the ditesseral polar-class. It is considered to be identical with chemically precipitated black mercuric sulphide, the density of both being 7.81. Cinnabar is of more common occurrence and is found as well-defined crystals and in the massive state. The crystals are assigned to the trigonal holoaxial class. The rhombohedral angle is 92°30' r correspouding to an axial ratio c/a of 1.1453. The crystals possess a very good cleavage parallel to the prism (21̄1̄)=(101̄0). The rotation of the plane of polarization, for red light traversing the crystal in a direction parallel to the optic axis, is 315° per millimetre, a value roughly eighteen times that of a similar thickness of quartz.
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