These are facet rough of lab created rutile, titanium dioxide. We have both near colorless (light yellow) and darker golden-honey material available.
This is rutile, and it has the highest dispersion of any transparent gem material. In practical terms that means it has the most insane fire you will ever see in a gemstone, throwing rainbows with the slightest provocation. It is simply impossible to capture on camera--they look good in a picture but great in person. It only has two downsides: its relatively low hardness of 6.5, a bit over tanzanite and suitable for pendant usage, and how difficult it is to get these days.
Crystals of rutile are grown for a few high end optical applications, particularly for very powerful prisms, as well as for use as a substrate to grow other crystals on. Production is fairly scarce today and often what we can get is of very low quality, so much of what we get is from old stock. However we recently got access to some high quality contemporary production--this material has a very light golden color and cuts absolutely unbelievable stones!
