Two Tricky Items

2007: I have gone through a similar situation during the course of my work, and I believe gemstones will continue to teach us one way or the other.

(via The Journal of Gemmology, Vol.IX, No.9, January 1965) G V Axon writes:

The pleasure one gets from guessing an identification and then proving it to be correct is always to be offset by the tendency to read the various gem instruments incorrectly with the guess uppermost in mind. Two stones recently gave the author a rather sharp lesson.

The first stone, about half-a-carat, was bright green, and with ‘horse-tail’ inclusions. The stone appeared pink with red flashes under the ordinary color filter, and even in ordinary light without the filter appeared to give off red flashes. The second stone, of some 22 carats, was quite a lively brown.

The first guess was demantoid garnet. The stone turned out to be chrome sphene. The second guess was heat treated amethyst. The stone was golden calcite. Neither chrome sphene nor golden calcite is seen frequently, the former because it is still rather rare, and the latter because it is so difficult to cut and so fragile.

Here were two very good examples of tricky looks. Of course, closer examination would have revealed that the horse-tail in chrome sphene did not appear to radiate, and that the doubling of the back facets in the calcite was apparent. The same would no doubt apply to a small clean chrome sphene examined under 10x lens.

Both stones were extremely tricky items, to say the least, for the horse-tail inclusion of demantoid has practically become its most single identification, yet here was a stone with very similar inclusions and almost identical in appearance. Thus ‘horse-tail’ inclusions will have to be watched rather more closely now.

As for golden calcite, so few specimens are to be seen that few jewelers will ever encounter them. Even so, heat treated amethyst is by now almost recognizable at sight—at least I thought it was, but after the shock of receiving a golden calcite and finding what appeared to be a heat treated amethyst, I have again learned the importance of never taking anything for granted, and of always making at least to tests, excluding the first ‘informed guess.’