Mohs Scale of hardness is a RELATIVE scale, not proportional. I mean by this that a mineral with the hardness of 8 will NOT be twice as hard a a 4. (For example, diamond is 40X harder than sapphire!).It is really a scale of relative "scratchability".

#1 is softest..................#10 is hardest

#1	Talc
#2	Gypsum
#3	Calcite
#4	Flourite
#5	Apatite
#6	Feldspar
#7	Quartz
#8	Topaz
#9	Corundum
#10	Diamond

Gemstones and Mohs Scale
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Diamond: .............10	Syth. Moissanite:.......9.5	Corundum: ................9
Cubic Zirconia:.. .8.5	Spinel: ........................8	Topaz: .......................8
Emerald: .......7.5 - 8	Almandite: ...............7.5	Rhodolite: ..........7 - 7.5
Pyrope: ........7 - 7.5	Spessartite: ...........7 - 7.5	Tourmaline: ........7 - 7.5
Iolite: ...........7 - 7.5	Quartz Group: .............7	Peridot: ..............6.5 - 7
Jadeite:.. ...6.5 - 7	Andradite: .............6.5 - 7	Scapolite: ..............6.5
Zircon (low): .......6.5	Tanzanite: ............6.5 - 7	Feldspars: ............6 - 7
Nephrite:.......6 - 6.5	Opal: ........................5.5	Lazulite: ...............5 - 6
Lapiz Lazuli:.....5- 6	Turquoise: ..............5 - 6	Sphene: .............5 - 5.5
Apatite: ...............5	Rhodochrosite: ............4	Coral .....................3 - 4

Fingernails are 2 1/2
Stainless Steel is about 5 1/2