2.64 ct. Indian ‘Iris’ Quartz
Color: Colorless / Play-of-Color
Clarity: Slightly Included
Origin: India
Cut: Partially Faceted Crystal
Treatments: None
Measurements: 9.4 x 9.2 mm
This most astonishing variety of Quartz came to light just a few years ago. Though this particular effect had been seen before, only when a fair amount of specimens came out of India did it get much notice. You can read the full story on mindat.org - it really is a somewhat amazing material. In fact, when you first see this odd play-of-color you feel almost certain that it must be the result of some treatment - a surface coating perhaps? It is in fact the result of interference between exceedingly thin layers of Brazil-law twin planes in the Quartz. Nearly all of this material was secured for the Japanese market (again, see the above article) and then, almost completely as specimens. 'Iris' Quartz is the most accepted name for this material now, though 'rainbow' Quartz and 'Lowell' Effect Quartz are also used.
The difficulty in producing faceted stones from this material was apparent immediately - the spectral colors are almost completely confined to the very surface of the crystal faces - one pass on a polishing wheel can sweep them away. Have a look at the photo below to see how the colors show up on an uncut crystal - again, very near the surface. This fascinating stone has preserved the effect by leaving the pavilion of the gem unfaceted - it is the natural crystal surface - while faceting the rest of the stone. The angle of light has to be just right here - it is not like an Opal where there is typically at least some color at most angles - you only see the flash at one, quite specific angle under direct lighting. The display is impressive, you can even catch greens and blues if you look through the pavilion. One of the few faceted examples!