Tips for Identifying Crystal Structure

I am very much an amateur, but I am trying to continue to improve my knowledge of gemstone and the various ways to identify them. This may be a dumb question but I don’t really understand how to identify the crystal formation of cut/worked stones. If unworked, it is often very easy, the shapes of the crystals are often very clear. But with worked/cut stones, I am not sure what to look for. Under magnification, I can sometimes see the crystal shapes of the stone itself or inclusions by looking for the various changes in internal symmetry inside the stone, but with most, I don’t know what to look for. I would be grateful for help with the basics of what to look for and how best to examine (ie, under magnification or held to the light, for example), or high level guidance on the broad categories of stone where crystal structure can be seen versus not seen, would be helpful.

To make a possibly dumb question even dumber (I appreciate your patience is this is very basic stuff), I see a crystal structure description for most gemstones in guides and on line, but as I mention above, I struggle to single out and see those. Do all gemstones have visible crystal structures (magnified or otherwise), or is the structure less a description for the purposes of identification, and instead something relevant mainly to cutting and working (which I do not do)? Thank you!

This is a great question. I have a very limited knowledge in this topic, and am curious what others have to say. Definitly will be following this thread.

Hey Paul, this is an interesting question. I cut diamonds, so I can give you some answers with respect to that gem. Diamond crystallizes in the cubic system. In rough crystals of gem quality their habit is generally octahedral, with 8 faces, or dodecahedral, 12 faces, or some variation or combination of the two. In industrial grades there are many varieties of crystal (or polycrystalline shapes). And, of course a cube has only 6 faces. This is all very confusing, because the crystal system really describes an internal atomic structure. And, to your point once the crystal is cut and polished into a gem even the external habit becomes almost totally obscured, unless the cutter left some ‘naturals’ visible on the finished piece.

To put it more simply, if you start with a cube, then facet its eight corners flat, it will become an octahedron. If you then facet the 12 edges of the octahedron flat, it becomes a dodecahedron. That is kind of how those crystals form in nature, all variations of a cube.

Naturals on a finished gem are remnants of the skin of the original crystal. They can leave clues, such as trigons, to suggest how the original rough formed.