Moh's Scale or Hardness

Named for the 19th century German mineralogist, Frederick Mohn who created it, the Mohs scale measures the hardness of minerals. The 10-point scale gauges the "scratch ability" of stones and minerals. It is by no means a balanced scale; the difference in hardness between 9 and 10 is greater than the difference between 1 (talc) and 9(sapphire). A high Mohs rating does not always mean that a gemstone is also tough. The emerald, for example, has a Mohs rating of 8.0, yet its crystal structure makes it more brittle and prone to cracking and chipping than members of the quartz family that have lower Mohs ratings. The precious metals gold and silver have a Mohs rating of about 4, which means that they can be scratched by many gemstones. Care should always be taken to store your jewelry separately to avoid scratching and damage.

How to Identificate gemstone

Hardness is the resistance a gem mineral offers to scratching or abrasion. Thus it's important property for durability. In 1824, the Austrian mineralogist Mohs selected 10 relatively common minerals and arranged them in order of increasing hardnesses from 1 to 10 as follows:

Specific Gravity (S.G.) is a number expressing the ratio between the weight of an equal volume of water at 4°c. The specific gravity of a gemstone is easily determined and can be an important characterizing property. To determine specific gravity, first weighed the gems fon in air and then in water. The difference in the two reading is the weight of the equal volume of water. Specific gravity can be expressed as follows :

weight in air
S.G. = ——–———————————
          weight in air - weight in water

For example, ruby weight 5.00 carats in air and 3.75 carats in water. The specific gravity is calculated as.

      5.00                         5.00
S.G.  =   ———————–  =  ————–   =   4
   5.00-3.75                    1.25

Refractive Index (RI) We can measure refractive of gemstone by use the refractometer.

Refractometer and Contact Liquid, Important Instrument to identify gemstones.