Diamagnetic minerals

Table 10.2 shows susceptibility values for selected diamagnetic minerals. For more detailed data, see Clark (1966), Lindsley et al. (1966), Melnikov et al. (1975), and Bleil and Petersen (1982). 

TABLE 10.2 Mass Susceptibility Kg and Volume Susceptibility k of Some Diamagnetic Minerals. 

Realgar is less diamagnetic than orpiment both in the solid form and in colloidal solution.8 The mineral is opaque to X-rays.9... 

The magnetization is negative and the materials have a pr-value of approximately 0.99995. Diamagnetism can only exist in an external field and among the materials which exhibit this phenomenon are Cd, Cu, Ag, Sn and A1203, as well as the minerals calcite CaC03 and fluorite CaF2. 

As a last example of a 1 1 structure derived from a cubic close-packed anion sublattice we mention that of the mineral sulvanite CU3VS4. Here, the copper atoms occupy three of the four positions of one set of tetrahedral holes, while the vanadium atom is located at one position of the other set. Thus, the anion is no longer tetrahedrally coordinated but has all four cation neighbours on the same side. In C113VS4 vanadium may be replaced by Nb and Ta and the sulphur by Se and Te (178). These compounds all are diamagnetic semiconductors containing monovalent copper and a pentavalent transition element, as does CuTaS3 (179) where Ta, however, is octahedrally coordinated. 

As best seen from Fig. 49 the structure of covellite CuS is composed of layers Cu+ — S2 — Cu+ which alternate with BN-like CuS layers. The latter are obviously responsible for the metallic properties of the CuS-type compounds. The diamagnetic CuS becomes superconducting at 1.62° K (215). Substitution of one third of the S by Se already shifts the transition to below 1° K (79). A replacement of the "divalent copper by nickel ( Cu2NiS3 ) failed (33). In the mineral idaite CusFeSg (507), however, one sixth of the copper atoms of CuS is replaced by iron atoms. 

With actinides one of the possible compositions found is M As2 like in ThAs2 in which each Th atom has 9 As neighbors. Three types of structures are important with transition metals and arsenic, CoAss, NiAs and those related to FeS2. CoAss is a diamagnetic semiconductor that occurs in the mineral skutterudite. It has a cubic structure related to that of ReOs but with distortions that result in planar AS4 rings. The NiAs structure is one of the most common MX structural types. In the structure each Ni is 8-coordinate and surrounded by 6 As and by 2 Ni atoms. The As atoms form a hep lattice in which the interstices are occupied by Ni atoms in a way that each As is surrounded by a trigonal prims of 6 Ni. ... 

Soft, white metal with bluish tinge. Emits a tin Cry on bending. Ductile, malleable, softer than lead, leaves a mark on paper. Quite stable in air. Crystallizes and is diamagnetic, d 7.3. mp 155. bp 2000". Sp heat 0.0568 cal/g/ C. Hardness (Mohs ) = 1.2. Unaffected by water attacked by mineral acids. Very resistant to alkalies. 

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