Here's a little horror story for everyone.
When I began my FGA courses one of the other students rushed into
class, very excited, with a huge plastic bag full of rough material
he'd bought that morning from someone he'd met in the college lunch
room. It had cost him a lot but it was a real bargain.
The bag was full of well formed tourmaline ctystals, beautifully
terminated and of the most exquisite greens and blues.
Then someone pointed out how strange it was that several of the
crystals were the same size and shape - identical! When we looked
more closely it was obvious that many of the inclusions were large
bubbles of air. When we checked the RI it confirmed that what the
"dealer" had sold him was glass that had been cast into sand. The
real crystals had been pushed into a bucket of sand and molten glass
poured into the cavity. Some of the sand stuck to the crystals making
them look very "real."
We looked for the dealer for a week or two but he never returned.