This scale shows a chart of relative hardness of various minerals (1 = softest, 10 = hardest).

Hardness Example

1
talc
2
gypsum
2.5
fingernail
3
calcite, a penny
4
fluorite
5
apatite
5.5-6.5
most glass
6
feldspar (spectrolite)
7
quartz (amethyst, citrine, agate)
6.5-7.5
steel file
7.5
garnet
8
beryl (emerald, aquamarine)
9
corundum (ruby, sapphire)
10
diamond