Hardness-Transparent Gemstones
Cochise College                          

Gemstone Properties
Virtual Museum of Geology
Hall of Gemstones
Geology Home Page

Roger Weller, geology instructor  ( wellerr@cochise.edu )
last edited:  10/24/07

hardness-transparent gemstones
The harder a gem is, the better it will be able to withstand being scratched.

The hardness of a gemstone is measured on its place on Mohs scale of hardness. 
10 on Mohs scale is the hardest known naturally occurring substance

     and the honor goes to diamond. 
Most faceted gems are in the range of 7 to 9 on Mohs scale. 
Some softer minerals are also used for gems because of their intense
     colors and patterns.
Gems below 6 in hardness must be treated with care. 

The hardest gems are at the top of this list.

diamond-10
 

sapphire-9

ruby-9
 

topaz-8

spinel-8

emerald-8 to 7.5

aquamarine-8 to 7.5

morganite-8 to 7.5

heliodor-8 to 7.5

alexandrite-8 to 5
 

andalusite-7.5

tourmaline (rubellite, indicolite, elbaite, etc.)-7.5 to 7

iolite-7.5 to 7

danburite-7.5 to 7

garnet (pyrope, rhodolite, grossularite, tsavorite, almandite,etc.)-7.5 to 6.5

zircon-7.5 to 6.5

amethyst-7

ametrine-7

citrine-7

rock crystal (quartz)-7

smoky quartz-7

tanzanite-7 to 6.5

peridot (olivine)-7 to 6.5

kunzite-7 to 6.5

hiddenite-7 to 6.5

kyanite-7 to 6
sillimanite-7 to 6
 

feldspar (orthoclase, labradorite, sunstone)-6

chrome diopside-6 to 5
 

sphene-5.5

moldavite-5.5

apatite-5

dioptase-5
 

fluorite-4