Not grow but still pressure related, I believe. Yes it's possible but not cost-efficient, so hasn't been pursued industrially.

Not well. The largest emeralds are found in a secret location in western NC. I have found all three in western NC, but only the sapphires were really good. I found a really large one at the Old Pressley Sapphire Mine outside of Ashville. It's a real mine. They excavate dirt and pile it up where you can fill up 5-gallon buckets of dirt yourself and then sluice them. One I found was as big as my thumb. I had one 8-carat cut out of it. It was blue-gray. The rubies and emeralds I found looked like pieces of old crayons and were pretty much worthless.