Although an entirely different species of mineral, Kyanite's usually medium-dark bluish bodycolors often resemble those of blue sapphire. In several markets across the world, many jewelry buyers often mistake one for the other. Experienced jewellers and gemologists however, can make use of a simple jewelry loupe to help them get a better grasp of what it is they are buying.
Kyanite tends to come with a lot of natural inclusions, even in mid-to-high market qualities. This can be a good thing and a bad-thing. On one hand, it helps gemologists separate this natural gem species from imitations like synthetic blue spinel, synthetic corundum and blue glass. On the other hand, some people automatically assume that a blue stone is sapphire if it shows very natural-looking fingerprint and crystal inclusions. Kyanite, just like sapphire can also be very strongly color-zoned.
In rough form, they can look very different. The main confusion for most people usually lies in separating faceted stones or polished cabochons set into jewelry. A little experience goes a long way though, and it's quite possible to find visual signs that can guide you in separating these two gemstones.
Kyanite as a mineral, possesses multiple planes of atomic weakness called cleavage planes. This property makes it easier for a stone to split in certain directions, and poses some threat to durability. You can sometimes observe this by looking at existing chips or fractures on a stone's girdle. Step-like fractures can indicate the presence of cleavage directions. Additionally, jewellers need to be more careful and pay extra attention when setting faceted kyanite onto mountings.
Sapphire does not possess any cleavage direction, and has a superior hardness of 9 on the Moh's scale, compared to Kyanite's direction-based hardness range of 4-7. This means that it can take a sharper and clearer polish on its facets as well.
Kyanite is much more affordable than sapphire, and can resemble the latter very strongly in color and internal profile. Commercial qualities though can show some colorless areas right next to blue zones of color. When these zonal areas are very strong and are arranged in certain positions, they can be a visual indication of the stone's identity for an experienced gem buyer.
Inclusions, fractures and color zones seem to have a tendency for parallel or 'striped' positioning in many kyanite specimens. Perpendicular elongated inclusions are also quite a common sight in many stone samples. Although despite visual characteristics being very helpful, the clear way to separate kyanite from blue sapphire is by testing for gemological properties like refractive index. This is a standard procedure for this separation, easily accomplished by a gemological laboratory.
Gemologists and labs can easily separate faceted kyanite from sapphire, as well as make the distinction between the latter and its man-made counterpart; synthetic sapphire.
Other possible confusions are tanzanite, synthetic forsterite, man-made blue spinel, blue glass, assembled triplet stones, iolite and other blue gemstone species. Each of these are valued differently in the gem trade, and it's always best to consult with a third-party gemologist on all matters of gemstone identity, grading and treatment history.
You can read more about blue sapphires and initial ways of separating it from more common imitations by reading one of our previous posts on the issue.
