Hi Howy,
To me "primary well-formed crystals" indicates gem quality probably better than commercial grade, but I think that we will need to await pictures and hopefully some cut stones to find out just how good they are. By "primary" I think this means that they have not been degraded by later metamorphic activity, and I read into what they are saying that they are distinct from and presumably better than the other deposits (but I may be wrong).
It may be dangerous to assume how large a cut gem might be from a particular crystal. Even for very good gem quality crystals, it all depends on what undesireable inclusions there might be in the stone that you might need to cut around, and to what degree they are cracked, although these days apparently a lot of cracks are "healed" in rubies. If the colour were uneven, or something of the like, some of the gem might be sacrificed to provide uniformity; a small perfect crystal would be more valuable than a larger, highly flawed one. For TGX's earlier emeralds, they were looking at only 5% yield on cut gems. For the rubies known before this field season, Rohtert was assuming 2.5-10% yield on cut stones. From what I've read, I believe the best, rare, well-formed world-class stones could theoretically be cut to gems of, say, up to 50% yield, but 20% might be an optimistic assumption for a very good, larger size crystal. If a 0.9 x 4 cm crystal were cut at 20% yield it would be a bit less than this number of carats (note that in cross-section, perfect crystals are not 4-sided squares, but rather 6-sided, but I assume 4 sided here) :
0.9 cm x 0.9 cm x 4 cm x .20 yield x 4 g/cm3 x 5 carats/g = 12.96 carats
probably divided into three or more stones. Cut rubies over 5 carat size are very rare. If we were to ever be so lucky, such a single tiny crystal would likely be worth many thousands, or even tens of thousands of dollars.
Of course, this is all speculation. Note that the optioners of the ruby properties (who had attempted a small hand-worked operation on some of the other ruby deposits) only got as much as 1.5 carats size from the rubies they cut. I do know that TGX are swamped with things to do so it may be a while before they cut stones from this deposit to show us, although I'm hoping there will be pictures of crystals in the rock soon (noting again that cut stones tend to look very different and significantly better than rough stones). |
