There is the easiest method to distinguish gemstones which, however, is not so easily applicable in real life, although it is still has a right to exist.
Thus, German mineralogist Friedrich Mohs has invented the method, which helps to distinguish a true hardness of each gemstone, using of not a sophisticated method of scratching.
Method is to define the resistance of a gemstone by scratching it, using another one. In the result, that gemstone, which was damaged is considered as inferior in hardness towards to its “adversary.”
Thus, Mohs has established the “Scale of Hardness,” named today in honor of his name.
Here is the Mohs Scale of Hardness, presented below:
Hence, the Diamond is the hardest mineral among all, because it can scratch each of inferior ones. Accordingly, the talc is the softest mineral and may be scratched by any of the minerals from 2 to 10 according to that scale. Thus, if a gemstone scratches the Quartz, but scratched by Topaz, its hardness would signify 7.5.
That’s why, when you’re trying to distinguish a gemstone on the jewelry markets of Thailand, India or Sri Lanka, the sellers always scratching the glass to prove you, that you hold in your hands true gemstone. They want to demonstrate you, that this mineral is harder than a glass, which is between 5.5 – 6.5, according to the Mohs scale.
However, this method will not be useful, to distinguish the difference between true and false Ruby or Sapphire, because unlikely the seller will scratch such valuable gemstones, using the Diamond, although it is the only method to define their hardness.
On the other hand, it is obvious, that any of the gemstones would surely scratch the glass, excepting maybe just only chrysolite, which is the softest among the popular gemstones. Although, such gems as: Turquoise, Opal and Lapis Lazuli are also soft and even inferior in hardness in comparison with chrysolite, therefore you’ve to be careful by choosing semi precious stones on the Oriental markets.
The same warning may be said on account of Zircon, due to its sufficient hardness for semi precious stone. Thus, it could be sold, in the likeness of the Diamond.
In order to help the consumer to orient oneself in such interesting question as the hardness of the minerals and gemstones, here is the full Scale of Hardness, invented by Mohs, presented below: