Rainbow lattice sunstone, also known as rainbow lattice, is a type of orthoclase feldspar that exhibits a rare combination of aventurescence, adularescence, and a distinctive iridescence lattice pattern. The iridescence lattice pattern consists of inclusions within the feldspar crystal.
Rainbow lattice sunstone 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 Caterpillar Mine. It is an area consisting of dry plains with rocky outcrops that lies in the Harts Range north-east of Alice Springs, Northern Territory, Australia. The primary source of this sunstone is covered by a single mining claim about 500 by 600 meters in size. Lower-quality Rainbow lattice sunstone is produced at another claim about 7 kilometers away from the primary source.
Rainbow Lattice Sunstone was identified at the GIA and declared a new gem variety in 1989. Initially, the study of this gemstone in 1989 concluded that the inclusions were made up of ilmenite (for the iridescence lattice and black triangles) and hematite (for the orange platelets). From 2017 to 2018, six samples of rainbow lattice sunstone were studied using electron microprobe analysis, X-ray diffraction analysis, and laser Raman spectroscopy. It was found that the host mineral is orthoclase (Or96Ab4), as previously reported in the literature and the inclusions causing the aventurescence are hematite. This research also discovered that the lattice patterns consist of orangey brown platelets of hematite and the black platelets consist of magnetite.
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. Hematite also forms as very thin blades that occur on one plane in different directions. These blades are oriented in different directions by a process known as lamellar twinning and also displays sagenitic twinning, which forms the lattice pattern.
Magnetite (Fe3O4) forms black, equilateral triangles. The magnetite that has no alteration is black with a metallic sheen.
Supply is extremely limited, and the only source is the tiny mine in the Harts Range, Northern Territory.
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