These are lab created emerald facet rough. Each is labelled with its gram weight and letter in the photo and they can be purchased individually.
Some pieces of rough have flaws like minor cracks and inclusions, including plumes of metallic copper. The color ranges from a lighter minty green to a deep rich green. I believe these emeralds are colored by a combination of copper and vanadium.
Emerald is one of the most classic gems, right up there with ruby and sapphire, but unlike them it is very difficult to grow in the lab. It can't be made by flame fusion or pulling methods, leaving the flux (slow and expensive and poisonous) and hydrothermal (slow and expensive and potentially explosive) methods. Still, it compensates for that with its incredible green color.
This one is a bit unusual for us since it wasn't grown for science--these are old vintage crystals that were grown in Russia for gem usage. However, I will note that occasionally lasers are made using an emerald crystal rod. The papers always have justifications about it being a good crystal matrix to hold chromium--but I suspect it has more to do with scientists proving that they can.
