First of all, make sure you have around 30m spare. [This is the way I did it, you do not need to follow this guide what so ever, it is blatently to help]
Inventory:
- Coins ~ Far bottom-right hand side of inventory.
- Chisel ~ 1 slot left, and 1 slot up from the coins.
Tactics:
> 1-15 = Opals
> 15 - 30 = Sapphires
> 30 - 50 = Emeralds
> 50 - 60 = Rubys
> 60 - 99 = Diamonds
How?:
Buy 10, 10, 5 of the gem you need. It will put 22 gems in your inventory, the last one will be on the left of your Chisel. Constantly click you Chisel, them the uncut gem.
Good luck on 99 Crafting!,
Xx Skill Xx