Inclusions are foreign matter (like another mineral or gas) enclosed within a gemstone. These irregularities occur during the growth process of a gemstone. Inclusions are common in all natural coloured gemstones. An eye-clean gemstone is either a rarity or a dream. As a matter of fact, they help determine whether a gemstone is natural or synthetic. Contrary to the common belief, gemstones may even enhance in value due to the presence of certain inclusions which add to their beauty, for instance, Opal and Blue Sapphires.
As mentioned earlier, inclusion-free gemstones are rare. A thorough microscopic examination will show that even an eye-clean gemstone has inclusions. Eye-clean precious gemstones, where the inclusions are not visible to the naked eye, are often very expensive. Prices for such gemstones can range into thousand of dollars per carat and beyond. These provide insights into the origin of the gemstone (mine/country), and whether the gemstone is synthetic or has been treated/enhanced. A gemstone too good to be true in terms of price/size/colour could likely be synthetic.
Inclusions can be internal or external. External inclusions refer to scratches, fractures or blemishes. They should be avoided, although soft gemstones may often contain scratches due to their extreme softness.
When the presence of an external specimen of a mineral is detected in the host mineral, we call it a solid inclusion. For instance, rutile deposits (external mineral) found in corundum (host mineral). However, any other foreign matter present during the growth of a gemstone also makes solid inclusions.
Often, cavities are detected in gemstones. These cavities can be filled with water, saline, liquid carbon monoxide, etc. Opals can have up to 30% liquid silica gel or hydrated silicon dioxide. This liquid inclusion is responsible for the rainbow hues in the gemstone.
When gas(es) occupy the cavities in a gemstone, we call it gaseous inclusions. The gases can be present independently or with liquid inclusion as well. Carbon monoxide is one of commonly occurring gas. These inclusions are fairly visible and identifiable because of the bubble formation within a gem's structure.
The presence of inclusions decides the clarity of gemstones. GIA, a reputed and trusted gemological institude, has divided the gemstones into three categories according to the inclusions present in them.
Type 1- No visible inclusions can be seen with the naked eye in the gemstones categorised as Type
Some of them are:Aquamarine, green chrysoberyl, tanzanite, morganite, blue zircon, green tourmaline.
Type 2- These stone are included, however, not all inclusions will be visible to the naked eye. Some of the gemstones in this category are:
Amethyst, ametrine, alexandrite, citrine, corundum (all sapphire and ruby), garnet, iolite, peridot, spinel, tourmaline (except green, pink or watermelon), and zircon (except blue).
Type 3- Gemstones falling in this cate gory are heavily included. Some of these gemstones are : Emerald, red beryl and red, pink and watermelon tourmaline.