Blue Topaz or Aquamarine?

Once I got back down to the bottom of the mountain (hill), I went back to the faceted gemstone seller and asked for a piece of Blue Topaz rough (I will call it this, in deference to her :). She sold me a light blue-green stone for five dollars.

I took it back to Phnom Penh with me and did some digging in my books. Along the right had side of this post are some views of this piece of crystal. I don't have the ability to measure its specific gravity or reflective index (that would put to rest the question easily), but I can list some arguments in favor and against it being Aquamarine based on what I learned or could see.

1) Aquamarine is not ruled out by its color, nor is Topaz. Both stones occur naturally in low saturated blue-green colored gems. On color it could be either.

2) Topaz and Aquamarine are known to occur in the same geologic setting, so there would be nothing surprising about Aquamarine being found in a location where mostly Topaz had been found until now. In fact Aquamarine is often found with Rock Crystal and with Smoky Quartz as Topaz is here. Nothing to rule out Aquamarine here.

3) The gem sellers all say that this light blue stone is more difficult to cut than is Quartz (there never was a question of whether this was quartz, quartz does not occur naturally in blue). They could not say if faceting the stone was more difficult or easier than for Topaz. The ones who believe that this stone is naturally occuring blue Topaz say that cutting is the same as cutting Topaz itself. If it were Aquamarine, it would be harder than Quartz, but possibly as hard as Topaz. Nothing determinative here. Easy to see why the cutters cannot tell. (Mohs is a 10-point scale and a standard gemological standard for measuring relative hardness. Diamond is 10.0.)

Quartz (Mohs=7.0); Aquamarine (7.5-8.0); Topaz (8.0)

4) To my mostly untrained eye, the crystal form of the stone appears to be hexagonal. If I am right, that might in and of itself rule out the orthorhombic Topaz.

5) The piece of crystal rough that I bought has striations parrallel to the long axis of the crystal. Both Aquamarine and Topaz are known to display that, though most of the Topaz crystal rough I saw at this site (and bought on a previous visit)  had been worn and pitted by their travel to a final alluvial deposit. On the other hand, and contradictorily, a lot of the quartz was so finely formed and unmarked that the gemstone dealers talked about how it looked as if it had been hand cut and polished!

So, until I can get the specific gravity of this stone measured (Aquamarine: 2.63 - 2.91, Topaz: 3.5 - 3.6, strangely different sources vary in the numbers they provide), or measure the refractive index on a cut stone, I may be out of moves.

Unless. Unless I go back and look at two cut stones, one clear and clearly Topaz, and the other light blue, same cut, same carat weight, and see if the Topaz is smaller (higher specific gravity).

Or. Or, ask for two stones that look to be the same physical size (volume) and see if the blue one has a lower carat weight.

Yeah. Yeah, I think that is what I will do. And if it appears to be Aquamarine, I will buy me a couple of stones. You should see the international retail prices for good color stones. :)