These are vivid green laser garnet gems cut in long hexagon RetroHex™ cuts! These are sold by carat size or range--exact size and proportions vary.
This is a simple style of long hexagon tablet cut reminiscent of all kinds of gems and crystals in old video games (thanks in part to the restrictions of pixel art)--in spite of its simplicity it makes for a lively gem with a very satisfying look.
Vanadium YAG is an exotic lab garnet--its pure composition gives it the most vivid green base color I have seen in any gem. Like Christmas garnet it functions as a Q switch to make lasers more powerful, and also makes an amazing gemstone. Some of these stones have fine inclusions which give them a slightly translucent look.
The sprite in the front photo is from Daniel Cook's classic space shooter game Tyrian 2000, used with permission from his site: Lost Garden.
