Gemstone crystals are formed over long durations of time under natural circumstances such as heat and pressure from earthly components. The availability of certain elements (essentially, the ingredients of a gemstone) determines its nature; will it be blue or green, or how rare it actually is. The addition and presence of these rare elements, makes the gemstone what it is; the presence of chromium gives Emerald its green color. The presence of Copper gives Paraiba Tourmaline its neon blue color.
Sometimes these trace elements can change over time, due to exogenous factors, and can cause color zoning – a common occurrence in Sapphires. An example is rutile needs that can form in Sapphire as well as Quartz. In Sapphire if enough of these needles collect in a stone, they actually become inclusions that are visible. In the rare instance, these inclusions can lead to the Star having the phenomenon of asterism – more commonly known as the Star-Sapphire.
Inclusions occur naturally, and to a student of gemology it provides clues of origin, a confirmation of its natural origin and a unique beauty which would not be replicated in another stone. In fact, in certain stones, such as Demantoid Garnet, the horse-tail inclusion will increase the value of the stone. The ‘new’ gemstone buyers undermine inclusions as flaws in stones, but fail to understand the natural process in which crystals form, and that these inclusions are the reason the stone has its unique colors and luster. A Kashmir Sapphire has its velvety unique look due to its silk inclusions! And these are the rarest of the natural corundums found! Ofcourse certain inclusions can cause the beauty of the stone to diminish, but this should be a case by case examination.