Does anyone know where I can find 2.5 mm mandarin garnet or
mexican faceted opal?
Try New Era Gems. They have smaller sizes in faceted Mexican
opal. Don't know if they go that small or not, but they may be
able to direct you if they don't. They also carry the most
incredible selection of different types of garnet rough I have
ever seen. Nice quality material at competative prices. They
offer a color catalog as well.
New Era Gems
14923 Rattlesnake Road
Grass Valley, Ca. 95945
They are very helpful and great people!