These are faceted hologram crystals, aka iron-doped lithium niobate. They are available in calibrated sizes and in fancy cuts. We have both light and dark-toned stones depending on the dopant level.
This is a really cool crystal--in particular iron-doped lithium niobate is grown for use in holographic storage. This is an emerging field (ok, it's been emerging since the 80s but still in progress) which allows data to be stored directly in a crystal lattice with reading and writing done via laser. It's an amazing idea whose time may yet come, but in the mean time these crystals broke during growth so we got them to repurpose as gems. Lithium niobate is a bright and fiery gem, and the added iron gives it a color ranging from a lighter peach to a deep orange-red.
Note that while lithium niobate makes an amazing gemstone its relatively low hardness of 5.5 limits it to pendant and earring usage in jewelry.
