I did a little research on the official Sims 3 site and found a couple of possible formulas to get spire cuts in other gems. I had no idea this was even possible, so thanks Tiberium Glow for asking about this.
Possible formulas:
"The way I get a Large Spire Cut Soulpeace is to use 4 pieces of Spire Cut Tiberium and 4 pieces of Emerald Cut Soulpeace. Using this formula there is only a 25% chance that you will create a Large Spire Cut Soulpeace, but this is the highest possible percentage, so you're better off saving your progress before you attempt it, because if it fails you can just reload. I have two pieces of Large Spire Cut Soulpeace, one is worth 227k and the other is worth 228k." -burnoutPERTH
"I did create a large OPAL spire by accident. Its very pretty! I was just foolin around and I had put two large spire tiberiums, and a whole lotta opal of any cuts, and presto! If I reinstall this game, if EA tries to fix the bugs, I will try for a Soulpeace large spire...its so much fun!" -LadyHCroft