Charlesite is a sulfate mineral of the
ettringite
Ettringite is a hydrous calcium aluminium sulfate mineral with formula: . It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of ...
group. Charlesite was named in 1945 after Dr. Charles
Palache mineralogist and professor at Harvard University for his work on minerals. This mineral is extremely rare, and when it is found it is often in crystal (but not gem) form. Its crystals are soft hexagonal, that can vary in color.
[http://rruff.info/doclib/am/vol68/AM68_1033.pdf Handbook of Mineralogy] Colors can range from clear to white, or even a pale yellow or pink. The brittle mineral's Mohs hardness is 2.5 with a specific gravity of 1.79. Though transparent to the eye the mineral has a white streak.
[http://webmineral.com/data/Charlesite.shtml#.Vl9UQuk0_wx WebMineral.com]
Occurrence
Charlesite has only been found in a few specific locations in the world. The first was its place of discovery in Franklin Mine in Franklin, Sussex County, New Jersey. It was located immediately above the 800 level, about 15 feet into the ore from the hanging wall. The ore mostly consisted of
franklinite
Franklinite is an oxide mineral belonging to the normal spinel subgroup's iron (Fe) series, with the formula ZnFe3+2O4.
As with another spinel member magnetite, both ferrous (2+) and ferric (3+) iron may be present in Franklinite samples. Diva ...
and
willemite
Willemite is a zinc silicate mineral () and a minor ore of zinc. It is highly fluorescent (green) under shortwave ultraviolet light. It occurs in a variety of colors in daylight, in fibrous masses and apple-green gemmy masses. Troostite is a v ...
and several other minor minerals. The crystals found at this location were up to 6mm in length and were suspected to have grown alongside
clinohedrite
Clinohedrite is a rare silicate mineral. Its chemical composition is a hydrous calcium-zinc silicate; CaZn(SiO4)·H2O. It crystallizes in the monoclinic system and typically occurs as veinlets and fracture coatings. It is commonly colorless, whi ...
crystals.
[http://rruff.info/doclib/am/vol68/AM68_1033.pdf Handbook of Mineralogy]
The other location where charlesite has been located is the Wessel's Mine, N' Chwaning Mines, and Kalahari Manganese Fields in Northern Cape Province, South Africa. The Wessel's Mine is thought to be the only source for charlesite to be found in gem quality.
[http://classicgems.net/gem_charlesite.htm ClassicGems.net]
Several of the other recorded places are Germany, Japan, Norway, Romania, and Slovakia.
[http://www.mindat.org/min-971.html MinDat.Org]
Uses
Due to its rarity, there are not very many uses for charlesite. Though there is not much of the mineral, one of the major uses for the ones that reach the standards is gems. Due to its softness it will not be found in much jewelry.
[http://rruff.info/doclib/am/vol68/AM68_1033.pdf Handbook of Mineralogy]
Some other uses could be for studying (the reasons for the rarity of the mineral), teaching
mineralogy
Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proce ...
classes, or even items for collectors or museums of rare minerals.
Composition
[http://webmineral.com/data/Charlesite.shtml#.Vl9UQuk0_wx WebMineral.com]
References
{{Reflist
Dunn P.J., Peacor D.R., Leavens P.B., Baum J.L.,1983, American Mineralogist, Charlesite, a new mineral of the ettringite group, New Jersey
[http://rruff.info/doclib/am/vol68/AM68_1033.pdf Handbook of Mineralogy]
Sulfate minerals
Trigonal minerals
Minerals in space group 159
Borate sulfates