How do I tell where the “c” axis on Topaz is and orientate it?
Sometimes Topaz can be hard to orientate because the stones have been water worn and the crystal shape has been worn off.
If there is a crystal shape (and/or a termination point) the cleavage is perpendicular to the growth direction, the “c” axis.
If the stones are water worn there is usually flat areas (sides) where the crystal has cleaved and tumbled (look for two flatish sides parallel to each other).
Also there is often a side that has the classic cleavage signs, like a deck of cards that someone has shaved a side off in a diagonal direction leaving a layered look. Sometimes looking with a loop will help you see them.
Topaz often has little silver inclusions (that are trapped between layers), that when you turn it in the light they will reflect when you reach the “c” axis.
As far as orientation for cutting, you want to be 7 degrees off of the “c” axis. Mostly you want to make sure that the deck of card type layers are cut so that the sides of the crystal (deck of cards) will not end up on a facet face, in particular a big facet.
A note of interest… Especially if you are buying Asian cut stones to use as preforms, I have often seen them cut with the table at zero (0). They cleave it clean and use the cleaved surface as their table, it is faster and one of the major facets is already polished for them. But if you are going to re-cut it then you need to be sure and orientate it the 7 degrees off of the “c” axis.