These are lab created emeralds cut in a variety of calibrated sizes. Some stones have minor cracks and inclusions, similar to a natural emerald, due to the hydrothermal growth method (or possible flux--some of these have inclusions that look more like flux growth).
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. We got these from a friend's old collection (something that was in the back of his safe for decades). They might have been grown by an Australian maker but we aren't sure about 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.
