Matlockite

Matlockite is a rarely occurring mineral from the mineral class of " halides ". It crystallizes in the tetragonal crystal system with the chemical composition PbFCl, that consists of equal parts of lead, fluorine and chlorine.

Matlockite usually develops transparent to translucent, tabular crystals with adamantine on the crystal surfaces and pearlescent on the cleavage surfaces. Also, lamellar, rosette-shaped or radial- mineral aggregates are known. Reiner matlockite is colorless and transparent. However, it may be caused by foreign admixtures also from light yellow to amber- yellow, yellow-orange or greenish color, its transparency decreases. The stroke color is, however, always white.

Special Features

Matlockite can easily be reduced to charcoal, with acid vapors will be emitted. It also dissolves readily in nitric acid. In dilute hydrochloric acid it is insoluble, whereas it is soluble to form Chloroplumbaten in concentrated hydrochloric acid.

Etymology and history

Probably the first mention of matlockite goes back to John Mawes descriptions of Mineralogy of Derbyshire in 1802.

The mineral was described scientifically, however until 1851 by Robert Philips Greg, who named it after lying in the vicinity of the type locality Matlock town, as the name Cromfordit ( Phosgenite today ) was already taken.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the matlockite belonged to the mineral class of " halides " and then to the Department of " oxyhalides " where he along with Bismoclit, Daubréeit, Rorisit and Zavaritskit the unnamed group III / D .09 was formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the matlockite also in the class of " halides ", there, however, in the department of " oxyhalides, hydroxyhalides and related double halides " one. This department is also further divided according to the conditions prevailing in the interconnect metals, so that the mineral is found according to its composition in the subsection " Using Pb (As, Sb, Bi) without Cu ", where his name to the " Matlockitgruppe " with system no. Forms 3.DC.25 and the other members Bismoclit, Daubréeit, Rorisit, Zavaritskit and Zhangpeishanit.

The mainly common in English-speaking classification of minerals according to Dana assigns the matlockite into the class of " halides " and there in the department of " halides ". Here it is also named the " Matlockitgruppe " with the system no. 09:02:11 and the other members Rorisit and Zhangpeishanit within the sub-division of finding " water clear and hydrated halides of the formula AX2 ".

Education and Locations

Matlockite forms as a secondary mineral in the oxidation zone of lead- containing deposits of galena ( galena, PbS ). Accompanying minerals is accordingly mostly galena, but also anglesite, barite, Boleite, Caledonit, Cerussite, Diaboleit, fluorite, Leadhillit, Phosgenite and sphalerite.

Overall matlockite has been (as of 2011) detected at about 30 localities. Apart from its type locality at Cromford Matlock mineral still occurred in England in the nearby " Bage Mine" at Bolehill in Derbyshire; at Crantock in Cornwall and in the "Water Bank Mine" at Ecton in Staffordshire.

In Germany matlockite is so far known only from the colliery Christian Levin at Essen in North Rhine -Westphalia and the only known locality in Austria is Waitschach in Carinthia.

A ten centimeters of very large crystal of Derbyshire is in the collections of the American Museum of Natural History. The Derby Museum and Art Gallery has a sample with a size of seven centimeters.

Other localities are Tasmania in Australia, Antofagasta and Tarapacá in Chile, Mengyin in China, Marvejols in France, Lavrion in Greece, the Italian province of Livorno, Kadoma in the South African province of Gauteng and Spruce in Elko County, Nevada, Spearfish in Zimbabwe, Argent Lawrence County, South Dakota, as well as several places in Arizona in the United States (USA).

Crystal structure

Matlockite crystallized tetragonal in the space group P4/nmm ( Raumgruppen-Nr. 129) with the lattice parameters a = 4.11 Å and c = 7.25 Å and two formula units per unit cell.