Tanzanite is a valuable and rare gemstone, but its value and rarity both increase with quality, particularly in untreated natural tanzanite.
This alluring gem owes its brilliance to its color – the more intense and saturated the blue, the greater its grade. More often than not, rough tanzanites are treated once they are mined, heated in crucibles to above five hundred degrees to bring out the most desirable blue-purple. If you happen to be a buyer, it is essential for you to understand the color grades of genuine tanzanite and be able to differentiate between different degrees of saturation and tone.
Let us start with natural rough tanzanite gemstones fresh out of the mines. These are most commonly found in shades of bronze or yellow-brown, sometimes with tinges of greens and greys. Of course this doesn’t necessarily imply that blue tanzanite does not occur naturally, but given its rarity and the fact that it is available in only a few mile radius in the whole world, naturally violet tanzanite is extremely rare. If you are getting a deal too good to be true online for naturally colored tanzanite, it probably isn’t authentic.
Tanzanite stones are from the zoisite family, and while zoisites are usually green, grey or pink, certain crystals found at the base of Mt. Kilimanjaro are heated naturally by the earth’s temperature, making them a shimmering blue with a slight purple hue.
Though naturally blue tanzanites are rare, a second best are stones which when mined have small portions of green, blue and purple shades.
When shopping for loose stones or tanzanite jewelry, of the four C’s color is one of the hardest to judge. Numerous unreliable sources, synthetic substitutes, heated and cobalt coated gems etc.have flooded the market, so when you shop you have to be able to differentiate between them.
Two factors come into play when judging the color of tanzanite, saturation and tone.
Saturation refers to, if the color of the stone is deep or shallow, in reference to the internal crystalline planes. If the color of a tanzanite crystal fills the gem, then it is of more value. This value isn’t only based on its beauty and desirability, but it also links to the rarity of a stone of such quality. Actually, only a few carats like these are mined in a whole year – the top 1% of the highest grade.
Next is the tone – the lightness or darkness of the stone. This is in reference to the stones color as well as the light it refracts. When assessing a stones tone, you must give preference to color tone over stones with dark accents due to cut. Often jewelers use cut and facets as a tactic to increase dark areas, but those are not fine grade gems.
Last but not the least is trichroism, the fact that a tanzanite when viewed from different crystalline angles exhibits different colors. Though this quality of the stone does not affect its grade or price, it is a useful mechanism to use when checking if a tanzanite gem is genuine.
Use saturation and tone levels as your basis for judging and assessing a tanzanite gems color, and then take it further from there. Don’t forget to get an authenticity certificate either!