emstones refer to the most beautiful and valuable types of stones on earth. There are natural mineral crystals such as crystals, rubies, sapphires, emeralds and so on; there are also natural monomineral aggregates, such as opals and a few organic materials such as pearls and corals, which belong to gemstones in a broader sense.

We can also classify gemstones according to their rareness. Among all types of gemstones, diamonds, rubies, sapphires and emeralds are regarded as four most precious stones; while mid-range gemstones such as aquamarines and tourmalines have been popular to collectors too thanks to their wonderful colors and meanings.

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