Sunstone
Encyclopedia
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.
The optical effect appears to be due to reflections from inclusions of red copper
, in the form of minute scales, which are hexagonal, rhombic
, or irregular in shape, and are disposed parallel to the principal cleavage-plane
. These inclusions give the stone an appearance something like that of aventurine
, hence 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."
, 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
.
and in eastern Lake County
north of Plush
. Only Oregon sunstone contains inclusions of copper
crystals. Oregon sunstone can be found as great as three inches wide. The copper leads to variant color within some stones, where turning one stone will result in manifold hues. The more copper within the stone, the darker the complexion.
On August 4, 1987, Oregon State Legislature
designated Oregon sunstone as its state gemstone by joint resolution.
Plagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
feldspar
Feldspar
Feldspars are a group of rock-forming tectosilicate minerals which make up as much as 60% of the Earth's crust....
, which when viewed from certain directions exhibits a brilliant spangled appearance
Aventurescence
In gemology, aventurescence is an optical reflectance effect seen in certain gems. The effect amounts to a metallic glitter, arising from minute, preferentially oriented mineral platelets within the material. These platelets are so numerous that they also influence the material's body colour...
; this has led to its use as a gemstone
Gemstone
A gemstone or gem is a piece of mineral, which, in cut and polished form, is used to make jewelry or other adornments...
. It has been found in Southern Norway, and in some United States localities. It is the official gemstone of Oregon.
Properties
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, in the form of minute scales, which are hexagonal, rhombic
Rhombus
In Euclidean geometry, a rhombus or rhomb is a convex quadrilateral whose four sides all have the same length. The rhombus is often called a diamond, after the diamonds suit in playing cards, or a lozenge, though the latter sometimes refers specifically to a rhombus with a 45° angle.Every...
, or irregular in shape, and are disposed parallel to the principal cleavage-plane
Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
. These inclusions give the stone an appearance something like that of aventurine
Aventurine
Aventurine is a form of quartz, characterised by its translucency and the presence of platy mineral inclusions that give a shimmering or glistening effect termed aventurescence....
, hence 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
Oligoclase
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite and anorthite . The albite:anorthite molar ratio ranges from 90:10 to 70:30.Oligoclase is a high sodium...
, though the effect is sometimes seen in orthoclase
Orthoclase
Orthoclase is an important tectosilicate mineral which forms igneous rock. The name is from the Greek for "straight fracture," because its two cleavage planes are at right angles to each other. Alternate names are alkali feldspar and potassium feldspar...
: 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 TvedestrandTvedestrand
is a town and municipality in Aust-Agder county, Norway. It is located in the traditional district of Sørlandet. The administrative center is the village of Tvedestrand....
, near Arendal
Arendal
is a town and municipality in the county of Aust-Agder, Norway. Arendal belongs to the traditional region of Sørlandet.The town of Arendal is the administrative center the municipality and also of Aust-Agder county...
, in south Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, where masses of the sunstone occur embedded in a vein of quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
running through gneiss
Gneiss
Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...
. Due to the discovery of large deposits in Oregon, Sunstone is now readily available.
Other locations include near Lake Baikal
Lake Baikal
Lake Baikal is the world's oldest at 30 million years old and deepest lake with an average depth of 744.4 metres.Located in the south of the Russian region of Siberia, between Irkutsk Oblast to the northwest and the Buryat Republic to the southeast, it is the most voluminous freshwater lake in the...
in Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, and several United States localities—notably at Middletown Township, Delaware County, Pennsylvania
Middletown Township, Delaware County, Pennsylvania
Middletown Township is a township in Delaware County, Pennsylvania, United States. The population was 16,064 at the 2000 census. The Pennsylvania State University has an undergraduate satellite campus located in the north-central portion of the township, while Neumann College, a private...
, Lakeview, Oregon
Lakeview, Oregon
Lakeview is a city in Lake County, Oregon, United States. The population was 2,294 at the 2010 census. It is the county seat of Lake County. Although it is an incorporated city, the municipal government refers to the community as "The Town of Lakeview", and bills itself as "Tallest Town in Oregon"...
, and Statesville, North Carolina
Statesville, North Carolina
Statesville is a city located in Iredell County, North Carolina, United States and was named an All-America City in 1997 and 2009. The population was 24,633 at the 2010 census...
.
The "orthoclase sunstone" variant has been found near Crown Point
Crown Point, New York
Crown Point is a town in Essex County, New York, USA. The population was 2,119 at the 2000 census. The name of the town is a direct translation of the original French name, "Point au Chevalure."...
and at several other localities in New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, as also at Glen Riddle in Delaware County, Pennsylvania
Delaware County, Pennsylvania
Delaware County is a county located in the U.S. state of Pennsylvania. As of 2010, the population was 558,979, making it Pennsylvania's fifth most populous county, behind Philadelphia, Allegheny, Montgomery, and Bucks counties....
, and at Amelia Courthouse
Amelia Courthouse, Virginia
Amelia Court House is a census-designated place in and the county seat of Amelia County, Virginia, United States. The population as of the 2010 Census was 1,099. Amelia Court House is also known as Amelia Courthouse and Amelia...
, Amelia County, Virginia
Amelia County, Virginia
As of the census of 2000, there were 11,400 people, 4,240 households, and 3,175 families residing in the county. The population density was 32 people per square mile . There were 4,609 housing units at an average density of 13 per square mile...
.
Sunstone is also found in Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
flows at Sunstone Knoll in Millard County, Utah
Millard County, Utah
Millard County is a county located in the U.S. state of Utah. In 2010, its population was 12,420. It was named for Millard Fillmore, thirteenth President of the United States. Its county seat is Fillmore and the largest city is Delta.-Geography:...
.
Oregon sunstone
A variety known as Oregon sunstone is found in Harney County, OregonHarney County, Oregon
-National protected areas:*Malheur National Forest *Malheur National Wildlife Refuge*Ochoco National Forest -Demographics:As of the census of 2000, there were 7,609 people, 3,036 households, and 2,094 families residing in the county. The population density was 1 people per square mile...
and in eastern Lake County
Lake County, Oregon
Lake County is a county in the high desert south central region of the U.S. state of Oregon, so named for the many lakes found within its boundaries, including Lake Abert, Hart Lake Reservoir, and Goose Lake. While Lake is among Oregon's largest counties, it is sparsely populated with 7,895...
north of Plush
Plush, Oregon
Plush is an unincorporated rural community in the Warner Valley of Lake County, Oregon, United States.The one notable attraction in the area is a hot spring located on the Hart Mountain National Antelope Refuge. Hart Mountain hosts many protected big game animals including the pronghorn antelope...
. Only Oregon sunstone contains inclusions of copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
crystals. Oregon sunstone can be found as great as three inches wide. The copper leads to variant color within some stones, where turning one stone will result in manifold hues. The more copper within the stone, the darker the complexion.
On August 4, 1987, Oregon State Legislature
Oregon Legislative Assembly
The Oregon Legislative Assembly is the state legislature for the U.S. state of Oregon. The Legislative Assembly is bicameral, consisting of an upper and lower house: the Senate, whose 30 members are elected to serve four-year terms; and the House of Representatives, with 60 members elected to...
designated Oregon sunstone as its state gemstone by joint resolution.