THE MOHS' SCALE OF HARDNESS

THE MOHS SCALE OF HARDNESS

The Mohs Scale, devised in 1812 by German mineralogist Friedrich Mohs (1773-1839), is used to compare the relative hardness of minerals.

The 2000+ different minerals existing are grouped into 10 levels of ascending hardness (those in each succeeding group being capable of scratching those preceding). Here's a well-known mnemonic sentence for remembering the scale:

" Those Girls Can Flirt And Other Queer Things Can Do "

being:
1.Talc (or mica)
2.Gypsum (rock salt)
3.Calcite
4.Fluorite (fluorspar)
5.Apatite
6.Orthaclase (feldspar)
7.Quartz
8.Topaz
9.Corondum
10.Diamond

Groups 1-2 can be scratched by a thumbnail.
Groups 3-6 can be scratched by a penknife.
Groups 7-10 will scratch glass.