Hardness of Minerals and Ceramics

See 90 Ed., p. 12-222, for hardness of minerals and ceramics (Mohs and Knoop scales) can be sorted in electronic versions. 

Milligan L. H., 1936, The impact abrasion-hardness of certain minerals and ceramic products, J. Am. Ceram. Soc., 19, 187-191. 

The distinctly differentiated results obtained, for example, for different faces of quartz or feldspar crystal, with clear observed differences depending on structure and compactness of the material under test, are an argument for wide use of the Mackensen blower in the study of engineering properties of rocks and ceramic materials and also in hardness estimation of minerals. 

Table 1. Hardness ranking of minerals and some prominent synthetic ceramic materials according to F. Mohs. In the case of the synthetic materials microhardness values are given in units of the Knoop scale. The microhardness variations result from variations in the grain size, the load of indentation, the phase composition and the used densification techniques. Modified after [152].

Such transformations have been extensively studied in quenched steels, but they can also be found in nonferrous alloys, ceramics, minerals, and polymers. They have been studied mainly for technical reasons, since the transformed material often has useful mechanical properties (hard, stiff, high damping (internal friction), shape memory). Martensitic transformations can occur at rather low temperature ( 100 K) where diffusional jumps of atoms are definitely frozen, but also at much higher temperature. Since they occur without transport of matter, they are not of central interest to solid state kinetics. However, in view of the crystallographic as well as the elastic and even plastic implications, diffusionless transformations may inform us about the principles involved in the structural part of heterogeneous solid state reactions, and for this reason we will discuss them. 

Hardness Estimation of Minerals, Rocks and Ceramic Materials... 

HARDNESS ESTIMATION OF MINERALS, ROCKS AND CERAMIC MATERIALS... 

Next to materials of the glass-ceramics type, many varieties of chalcedony, such as agate, carneol, onyx, sardonyx, heliotrope and jasper, exhibit similar changes in hardness resulting from different consolidation of the cryptocrystalline structure of silica among mineral individuals. 

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