Binghamite (also called silkstone and cuyunite) is a type of

chalcedony Chalcedony ( or ) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic ...

found only on the

Cuyuna Range The Cuyuna Range is an inactive iron range to the southwest of the Mesabi Range, largely within Crow Wing County, Minnesota. It lies along a line between Brainerd, Minnesota, and Aitkin, Minnesota. The width ranges from 1 to 10 miles (1.6 to 1 ...

(near

Crosby Crosby may refer to: Places Canada *Crosby, Ontario, part of the township of Rideau Lakes, Ontario *Crosby, Ontario, a neighbourhood in the city of Markham, Ontario England *Crosby, Cumbria *Crosby, Lincolnshire *Crosby, Merseyside **Crosby (UK P ...

) in Crow Wing County,

Minnesota Minnesota ( ) is a U.S. state, state in the Upper Midwestern region of the United States. It is bordered by the Canadian provinces of Manitoba and Ontario to the north and east and by the U.S. states of Wisconsin to the east, Iowa to the so ...

.Binghamite on Mindat
/ref> The stone occurs near deposits of

iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron is usually found in the f ...

Description

Mining in the area uncovered deposits of the stone, but since mining operations were discontinued in the area many years ago the stone has become fairly rare. The stone has areas that are highly

chatoyant In gemology, chatoyancy ( ), also called chatoyance or the cat's eye effect, is an optical reflectance effect seen in certain gemstones. (Historically, the term has applied specifically to gems; in woods and other materials the effect is more ...

similar to pietersite or

tiger's eye Tiger's eye (also called tiger eye) is a chatoyant gemstone that is usually a metamorphic rock with a golden to red-brown colour and a silky lustre. As members of the quartz group, tiger's eye and the related blue-coloured mineral hawk's e ...

. It is a variety of

with fibers of

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the α- polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

usually in colors of red, gold, and black. The highest quality binghamite compares with pietersite for color and

chatoyancy In gemology, chatoyancy ( ), also called chatoyance or the cat's eye effect, is an optical phenomenon, optical reflectance effect seen in certain gemstones. (Historically, the term has applied specifically to gems; in woods and other materials ...

. When the stone's pattern is arranged in parallel bands it is called silkstone. Binghamite is named after William Bingham, a

lapidarist Lapidary () is the practice of shaping stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameos), and faceted designs. A person who practices lapidary techniques of cutting, grinding, and polishin ...

, who discovered it in 1936.

References

*{{cite book , last= Schumann, first=Walter , title=Gemstones of the World , year=2007 , publisher=Sterling Publishing Company, Inc. , isbn=1-4027-4016-6 Crow Wing County, Minnesota Geology of Minnesota Agates