Answer: Tourmalines can pose challenges, even for experienced faceters. Your choice of lap and facet progression can play a critical role in whether or not your stone will shatter.
Selecting the Right Lap
I have a friend who facets both nodules and crystals of tourmaline. I shared your question with him. He’s had no problem cutting tourmaline nodules. However, he has experienced the same problem you described, only with Nigerian green tourmaline crystals. He had preformed them with 260 grit diamond. My friend solved the problem by not touching the crystals, during preforming or cutting, with any courser grit than a 1200 flat lap. He said it’s slower, but you won’t end up with a bunch of aquarium gravel.
Hope this helps,
Cutting Tourmaline Facets in a Safe Progression
I have some tips for cutting tourmaline gemstones that might reduce their likelihood of shattering.
Never cut the girdle first. Try to cut as much of the pavilion as possible, while leaving the crystal faces as intact as you can, before establishing a girdle. These natural surfaces serve to hold the crystal together. Removing them prematurely could cause the crystal to lose integrity.
I do think the 260 grit is the ultimate tourmaline killer. It probably does have something to do with sonic vibration. I’ve had no problem with Afghan tourmalines until I used the 260. It does make an odd ringy sound.
Hope this helps eliminate your cutting tourmaline woes.