Rainbow lattice sunstone
The inclusions (internal features) are referred to as: the result of crystallographically oriented exsolution crystals within the feldspar mass.
Whilst the initial testing of the stones inclusions conducted in 1989 concluded that the inclusions were made up of ilmenite (for the black blades and triangles) and hematite (for the orange platelets), with the advancement in technology over the last 3 decades, a recently conducted more in depth analysis has found the black blades and triangle inclusions in Rainbow Lattice to be magnetite.
A paper with these results will be published soon by authors from the Gemmological Institute, China University of Geosciences (Wuhan) and it will be published in The Journal of Gemmology by Gem-A.
Hematite (Fe2O3) which are small mainly yellow to deep orange platelets which can be hexagonal shape and are generally in one plane within the feldspar. This effect is called aventurescence or "sunstone effect" which gives some of the gems an orange glow.
Magnetite (Fe3O4) iron oxide which creates the lattice effect. This forms as a very thin blades that occur in one plane at different levels. These blades orientate (north/south) in different levels by a process known as lamellar twinning and also displays “Sagentic twinning”, which forms the lattice pattern. The magnetite inclusions in many cases have oxidized or altered through geophysical processes to give the iridescence or rainbow effect across the lattice patterning. The magnetite that has no alteration remains black with a metallic sheen. The magnetite also predominantly forms equilateral triangles and the lattice pattern has triangular terminations.
It was first discovered in late 1985 by Darren Arthur and Sonny Mason, on a small claim owned by Mason. The original source is located at what is now known as the “Rainbow Serpent Mine”, in the Harts Range Northeast of Alice Springs, Northern Territory, Australia.
It was identified at the GIA and declared a new gem variety in 1989.
After Mason's death, Arthur went to co-found Asterism Gems, a company which was set up to market and sell the gemstones.
- Gems & Gemology Vol XXV - Spring 1989 p.47