My SIL just got a beautiful tazanite ring…the jewelr told her that this gemstone is only found in one location in east Africa (Tanzania), and that the deposits of the stone are limited.
Is this true? Why would a mineral not exist in other places aound the world?
Or is this a DeBeers type strategy (keep the price up by endlessly advertising rarity)?
Most gemstones have multiple sources-I find it hard to accept that there is only one place in the world where this stuff (Tanzanite) is ound.
The Jewellery Channel peddles this particular line - Tanzanite is only available from one area of Tanzania and is ultimately limited in quantity. I have no way of verifying this and TJC is (or is affiliated with) the main Tanzanite wholesaler so may have a vested interest in this story; however, if it’s a lie it’s a consistent one. I would assume that anyone mining it elsewhere would also have a vested interest in maintaining the story to keep the price from plummeting (as it likely would if supply was discovered to be greater than previously thought).
Not to shill for TJC, by the way, but their prices are frequently substantially lower than the main jewellery stores due to the wholesaler connection - useful for comparison of markup, if nothing else.
It is only found in Tanzania. Here is a page on the geology.
It’s not that uncommon for a mineral to only be found in one area: another example is a rare form of fluorite, “blue john”, or “Derbyshire spar”, that’s only found in the caves surrounding Castleton, in Derbyshire.
Well, it’s one – the most commercially valuable – variety of zoisite, which is found at multiple locations throughout Europe and Africa. Wikipedia’s tanzanite article seems focused on the Indian precious stone industry and the conflicts between Tanzania and India over it.
Tanzanite’s only one form of zoisite, which occurs in several places around the world. The more common variety often occurs in the metamorphic rock anyolite; it’s one of the most striking and valuable of decorative stones. Against a medium green background, somewhat darker than mint ice cream, there are bright red ruby crystal inclusions. The rubies aren’t gem quality and can’t be used on their own, but their appearance in the rock is remarkable.
Tanzanite is s-o-o yesterday. 
Seriously, it was truly hottest about 6-15 years ago. It was new then, and the really, really deep colored stuff in large sizes was pretty pricy. And it sold well. Over the years, the demand for it has faded. Now, we hardly sell any at all. Not that it isn’t one of the more striking gems out there, and it’s actually rather scarce, at least the deep colored, inclusion free larger pieces.
The department store jewelry counters and “home shopping” types of retailers always offered the pale colors. Much more common and not very valuable. Resale almost nil.
The problem with colored stones is, when you get tired of it, the resale is pretty dificult.
I bought one for my wife’s wedding ring about 25 years or so ago (I can’t remember exactly) and was told at the time that it was only mined in one place. So, the sales pitch has been the same for over two decades now.
Diamonds never appealed to us and she picked this out instead. The color is very nice and deep. It was inexpensive at the time and we weren’t making a financial investment… just an emotional one. So far it has worked pretty well I guess.