Changes

If the mineral under examination is scratched by the knife-blade as easily as calcite its hardness is said to be 3; if less easily than calcite and more so than fluorite its hardness is 3.5. In the latter case the mineral in question would be scratched by fluorite but would itself scratch calcite. It need hardly be added that great accuracy is not attainable by the above methods, though, indeed, for purposes of the determination of minerals, exactness is quite unnecessary.

If the mineral under examination is scratched by the knife-blade as easily as calcite its hardness is said to be 3; if less easily than calcite and more so than fluorite its hardness is 3.5. In the latter case the mineral in question would be scratched by fluorite but would itself scratch calcite. It need hardly be added that great accuracy is not attainable by the above methods, though, indeed, for purposes of the determination of minerals, exactness is quite unnecessary.

It should be noted that minerals of grade 1 have a [[greasy]] feel to the [[hand]]; those of grade 2 are easily scratched by the [[fingernail]]; those of grade 3 are rather readily cut, as by a knife; of grade 4, scratched rather easily by the knife; grade 5, scratched with some difficulty; grade 6, barely scratched by a knife, but distinctly by a file - moreover, they also scratch ordinary [[glass]]. Minerals as hard as quartz (H. = 7), or harder, scratch glass readily but are little touched by a file.

It should be noted that minerals of:

 

*grade 1 have a soft, [[greasy]] feel to the [[hand]] like [[talc]] and [[graphite]], and flakes of it will be left on the fingers,

*grade 2 are easily scratched by the [[fingernail]], as a cleavage piece of [[gypsum]],

*grade 3 are rather readily cut, as by a knife and just scratched by a copper coin but is not scratched by the fingernail,

*grade 4, scratched rather easily by the knife but is not so easily cut as [[calcite]],

*grade 5, scratched with some difficulty,

*grade 6, barely scratched by a knife, but distinctly by a file - moreover, they also scratch ordinary [[glass]],

*minerals as hard as quartz (H. = 7), or harder, scratch glass readily but are little touched by a file.

=Sources=

=Sources=

*Chesterman, Charles W. ''The Audubon Society Field Guide to North American Rocks and Minerals'', Alfred A. Knopf: New York (1987)

*Chesterman, Charles W. ''The Audubon Society Field Guide to North American Rocks and Minerals'', Alfred A. Knopf: New York (1987)

*Dana, Edward S. and Ford, William E. ''Dana's Textbook of Mineralogy - Fourth Edition'', John Wiley and Sons: New York (1932)

*Dana, Edward S. and Ford, William E. ''Dana's Textbook of Mineralogy - Fourth Edition'', John Wiley and Sons: New York (1932)

[[category:Minerals]]

[[category:Minerals]]