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The effect appears to be due to reflections from enclosures of red haematite, in the form of minute scales, which are hexagonal, rhombic or irregular in shape, and are disposed parallel to the principal cleavage-plane. These enclosures give the stone an appearance something like that of aventurine, whence sunstone is known also as "aventurine-feldspar."
Sunstone is not common, 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. It is found also near Lake Baikal, in Siberia, and at several localities in the United States, notably at Middletown Township, Delaware County, Pennsylvania, and at Statesville, North Carolina.
The feldspar which usually displays the aventurine appearance is oligoclase, but the effect is sometimes seen also in orthoclase: hence two kinds of sunstone are distinguished as "oligoclase sunstone" and "orthoclase sunstone." The latter has been found near Crown Point and at several other localities in New York, as also at Glen Riddle in Delaware County, Pennsylvania, and at Amelia Courthouse, Amelia County, Virginia. Sunstone is also found in Pleistocene basalt flows at Sunstone Knoll in Millard County, Utah.
A variety known as Oregon sunstone is found in Harney County, Oregon and in eastern Lake County north of Plush. Only Oregon sunstone contains inclusions of copper crystals. Oregon sunstone can be found as large as three inches across. The copper leads to varying color within some stones, where turning one stone will result in multiple colors. The more copper within the stone, the darker the complexion.
This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Sunstone". A list of authors is available in Wikipedia.|