Jewelry Birthstones Wizard
“How to Buy Birthstones Like a Pro” by padre art
Mohs Hardness Scale
by: padre art
The Mohs hardness scale is a more or less accurate system for determining the hardness of gem and mineral specimens. This technique was defined in the early 1800’s by the German mineralogist Friedrich Mohs, but the concept of scratching one rock against another to determine its utility for certain purposes is ancient.
It was written about as early as 300 BC by Theophrastus and reiterated by Pliny the Elder before 100 AD although people had been sharpening jade and other stones against one another long before the written word.
The Mohs hardness scale is made up of ten minerals that were considered commonly available in the early 19th century. While these same minerals make up the scale today, the system has been changed somewhat to take into account more subtle variations.
The reason the Mohs hardness scale is not completely accurate has to do with naturally occurring differences in the same mineral type. Most mineral types fit within a range on the existing scale of ten.
Along with that is the inconsistent changes between one number on the scale and the next. For the lower numbers the difference is a factor of three, gypsum is three time as hard as talc and calcite is three times as hard as gypsum.
For the numbers 4 through 9 each is roughly twice as hard as the previous but the diamond, #10, is four times as hard as corundum.
Below is a modified Mohs hardness scale. Half steps are added for more accuracy and the number in parenthesis give the approximate difference in hardness as the Mohs hardness scale ascends. You can use this to find your birthstone.
1) Talc
2) Gypsum (3)
2.5) Gold, silver, copper, fingernails
3) Calcite (3)
3.5) Coral
4) Fluorite (2+)
4.5) Platinum, iron
5) Apatite (2) - amber
5.5) Turquoise, lapis lazuli, opal, glass
6) Feldspar (Moonstone) (2) - nephrite,
6.5) Jadeite, peridot, tanzanite, zircon
7) Quartz (1.25) - amethyst, hardened steel
7.5) Garnet, tourmaline
8) Topaz (2) - spinel, beryl (emerald & aquamarine)
8.5) Chrysoberyl, cubic zirconia
9) Corundum (2) - ruby, sapphire
10) Diamond (4)
Thanks to modern technology there are extremely accurate ways to measure the differences in minerals and allow for very accurate determination of hardness, crystal structure, molecular bonding strength and other factors.
Using the Mohs hardness scale is still the easiest method for mineralogists to classify different mineral types and for all of its inaccuracies it works as well in the modern day to day world as scratching one rock against another did for our ancient ancestors.
Mohs Hardness Scale
