Caledonite
- Caledonite
- Cupreous sulphato carbonates of lead
- Copper -containing sulfur - carbonate of lead
Caledonit is a rarely occurring mineral from the mineral class of " sulfates ( and relatives ) ." It crystallizes in the orthorhombic crystal system with the composition Pb5Cu2 [( OH) 6 | CO3 | (SO4 ) 3], and is therefore chemically seen a lead-copper sulfate with additional hydroxyl and carbonate anions.
Caledonit usually develops transparent to translucent crystals with acicular to prismatic habit and resin to glass-like sheen on the surfaces. Often the crystals are well positioned to radialstrahligen or tufted aggregates. The color of the mineral varies between dark green and tension lighter bluish green, the stroke color, however, is light green.
With a Mohs hardness of 2.5 to 3 Caledonit belongs to the medium-hard minerals that are similar as the reference mineral calcite (3 ) can be scratched with a copper coin.
Special Features
Caledonit is how the chemically similar minerals Susannite, Leadhillit and Macphersonit, foaming soluble in nitric acid with evolution of carbon dioxide. Here, a white precipitate of lead sulfate forms.
Etymology and history
Caledonit was first discovered at Leadhills in South West Scotland and described in 1820 by Henry James Brooke ( 1771-1857 ), who first described the mineral as Cupreous sulphato carbonates of lead. A year later accepts Karl Caesar von Leonhard this designation in its 2nd edition of his work Handbook of Oryktognosie, translated, however, with copper -containing sulfur - carbonate of lead into German.
When August Breithaupt in 1832 his " complete characteristics of the mineral system " was published, he is based in the designation of the mineral rather on its crystal structure and describes it as Prismatic copper lead - spar.
His final name Caledonit or Caledonite finally got the mineral by François Sulpice Beudant, who named it based on its type locality according to the Latin- Celtic word for Scotland.
Classification
In the now outdated but still in use 8th edition of the mineral classification by Strunz the Caledonit to the mineral class of " sulfates, selenates, tellurates, chromates, molybdates, tungstates " and then to the Department of " water clear sulfates with foreign anions " belonged, where he served as single member of the independent group VI/B.09 formed.
The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the Caledonit also in the class of " sulfates ( selenates, tellurates, chromates, molybdates and tungstates ) " and then in the Department of " Sulfate ( selenates, etc.) with other anions, without H2O" a. This division, however, is further divided according to the size of the cations involved, so that the mineral is found according to its composition in the subsection "With medium -sized and large cations " where it also forms the unnamed group 7.BC.50 the only member.
The mostly commonly used in English-speaking classification of minerals according to Dana assigns the Caledonit in the class of " sulfates, chromates and molybdates ", to which, however, also the child selenates, tellurates, Selenite, Tellurite, sulfites and chromates belong. Caledonit here belongs to the Department of " Composite Sulfate " and is the only member of the unnamed group 32.03.02 within the sub-division of " Composite Sulfate with polyanionic formula (anhydrous) " to find.
Education and Locations
Caledonit forms as a typical secondary mineral predominantly in the weathering zone of lead and copper deposits. Accompanying minerals include anglesite, azurite, Brochantite, Cerussite, Leadhillit, Linarit and malachite.
As a rather rare mineral formation can Caledonit at different sites may sometimes be abundant indeed, but overall he is not widespread. As known (as of 2011) apply worldwide so far around 300 localities. Apart from its type locality Leadhills, which is also known for particularly large Caledonitkristalle of up to 2 cm in size, the mineral in the UK yet occurred at many other locations in England, Scotland and Wales.
Known due to exceptional Caledonit discoveries include the " Mammoth Mine" in Pinal County (Arizona ), and the "Blue Bell Mine" in San Bernardino County ( California ) in the U.S., where crystals between 1.5 and 2 cm in size found were. In addition, are known from the Tchah - Mille- mine at Anarak in the Iranian province of Esfahan still Druze findings with well-developed crystals.
In Germany Caledonit found so far mainly in the Black Forest in Baden- Württemberg, but also at the Hohenstein at Laudertal and in the " pit Association " in Eisenbach in Hesse, in several places in the Harz Mountains from Lower Saxony to Saxony- Anhalt, in several mines of the Bergisch country, Ruhr area, Sauerland winner country in North Rhine-Westphalia, in several places of the Eifel and Westerwald Rhineland -Palatinate and in the pit "Holy Trinity " in Zschopau in Saxony.
In Austria several localities in Carinthia, Lower Austria, Salzburg and Styria are known in Switzerland, however, only " Les Moulins Mine" at Saint- Luc VS in the canton of Valais.
Other localities lie among others in Argentina, Australia, Belgium, Bolivia, Bulgaria, Chile, China, France, Greece, Ireland, Italy, Japan, Canada, Mexico, Morocco, Namibia, Norway, Pakistan, Portugal, Romania, Russia, Spain, South Africa and the United States of America.
Crystal structure
Caledonit crystallizes in the orthorhombic space group Pnm21 ( Raumgruppen-Nr. 31) with the lattice parameters a = 7.15 Å; b = 20.09 Å and c = 6.56 Å and two formula units per unit cell.