| Sunstone | |
|---|---|
 |
|
| General | |
| Category | Crystal |
| Chemical formula | sodium calcium aluminum silicate (Ca,Na)((AI,Si)2Si2O8) |
| Identification | |
| Color | Clear, yellow, red, green, blue and copper shiller |
| Crystal habit | Euhedral Crytals, Granular |
| Crystal system | Triclinic |
| Twinning | Lamellar |
| Cleavage | 001 Perfect, 010 Good |
| Fracture | Conchoidal |
| Mohs scale hardness | 6 - 7.2 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent to Translucent |
| Density | 2.64 - 2.66 |
| Optical properties | Double Refractive: weak to medium |
| Refractive index | 1.525 - 1.58 |
| Dispersion | Weak |
Sunstone is a plagioclase feldspar, which when viewed from certain directions exhibits a brilliant spangled appearance; this has led to its use as a gemstone. It has been found in Southern Norway, and in some United States localities. It is the official gemstone of Oregon.
Contents |
Properties
The optical 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." The optical effect called shiller and the color in Oregon Sunstone is due to copper. In the middle part of this crystal, it sparks a lot, and usually has a dark color in the middle, and the color becomes lighter as it becomes the outer part.
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."
Distribution
Sunstone was not common until recently. 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. Due to the discovery of large deposits in Oregon, Sunstone is now readily available.
Other locations include near Lake Baikal in Siberia, and several United States localities—notably at Middletown Township, Delaware County, Pennsylvania, Lakeview, Oregon, and Statesville, North Carolina.
The "orthoclase sunstone" variant 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.[1]
Oregon sunstone
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.[2] 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.[3]
On August 4, 1987, Oregon State Legislature designated Oregon sunstone as its state gemstone by joint resolution.[4][5]
One of the leading mining operations is the "Dust Devil Mine", founded by rockhounds and which started selling Oregon sunstone in 1996. Many award winning gem cutters and carvers dig their own sunstone at the mine before cutting and carving them. Stones of over 300 cts have come from the pit.[6] The largest producing Oregon Sunstone mine is the Ponderosa Mine north of Burns, Oregon.
References
- ^ Sunstones at Sunstone Knoll, Millard County. Utah Geological Survey, accessed September 14, 2007.
- ^ McClellan, Jan. Oregon Sunstone, Fact and Fancy. Designer Jewelry.
- ^ Oregon Sunstone - Official State Gemstone. Nature of the Northwest: Rock Hounding, accessed September 13, 2007.
- ^ Chapter 186 – State Emblems; State Boundary 2005 Oregon Revised Statutes
- ^ "Oregon Symbols". SHG Resources. http://www.shgresources.com/or/symbols/gemstone/. Retrieved 2007-09-14.
- ^ Dust Devil Mine
This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed (1911). Encyclopædia Britannica (Eleventh ed.). Cambridge University Press.
External links
- Mineralogy Database
- Saab, Patricia. Oregon Sunstone in the Oregon Encyclopedia
|
|||||||||||||||||||||||||||||||||||||||