It would be difficult to believe that there are as many as 300 minerals which are classified as gemstones. We usually refer to all such gemstones as semi precious and precious stones, but technically there is not too much of difference between precious and semi-precious. That is why the Federal Trade Commission in the United States of America is considering doing away with those two terms. Yet, it is instructive for us to note that as per the currently existing distinction, there are only 4 gemstones which are considered to be precious stones.
Sapphire: This colorless crystalline form of alumina is valued highly when it attains the bluish hues due to the presence of certain quantities of corundum. The molecules are arranged in a hexagonal crystal lattice structure giving it a hardness index of 9 (as compared to 10 for diamond) on the Mohs scale.
Ruby: The color red is the defining color for ruby, and its shades vary from rich darkish red to pigeon blood red, and even include pinkish red. The presence of traces of the mineral chromium causes the red color of rubies. Rubies have a hardness of 9 on the Mohs scale.
Emerald: The fourth precious stone follows the natural progression of white (diamond), blue (sapphire), and red (ruby). It is a green colored precious gemstone which owes its color to traces of the mineral called beryl. The hardness of emerald is less than 8 on the Mohs scale.
You can get attractive jewelry made using these precious stones in a good online jewelry store like Giliarto.
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