After much controversy and debate, most of these gemstones, allegedly sourced from China, were subsequently discovered to have been artificially colored by a copper diffusion process. In the early 2000s, a new variety of red or green gemstone resembling sunstone and known as "Andesine" appeared in the gem market. Other locations include near Lake Baikal in Siberia, and several United States localities-notably at Middletown Township, Delaware County, Pennsylvania Plush, Oregon and Statesville, North Carolina. Previously the best-known locality being Tvedestrand, near Arendal, in south Norway, where masses of the sunstone occur embedded in a vein of quartz running through gneiss. The feldspar which usually displays the aventurine appearance is oligoclase, though the effect is sometimes seen in orthoclase: hence two kinds of sunstone are distinguished as "oligoclase sunstone" and "orthoclase sunstone". The middle part of this crystal sparkles, and usually the color is darkest in the middle and becomes lighter toward the outer edges. The optical effect is called schiller and the color of Oregon Sunstone is due to copper. These inclusions give the stone an appearance something like that of aventurine, hence sunstone is known also as "aventurine-feldspar". The optical effect is due to reflections from inclusions of red copper, hematite, or goethite, in the form of minute scales, which are hexagonal, rhombic, or irregular in shape, and are disposed parallel to the principal cleavage-plane.
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