674 PYRITES 



sufficiently free from other substances may be utilised as an iron ore. This is a recent 

 application, the material so obtained being known as purple ore, or blue billy. When 

 exposed to moist air, pyrites becomes rapidly changed into sulphate of protoxide of 

 iron, which, by a further absorption of oxygen, gives rise to numerous complicated 

 minerals, containing peroxide of iron and sulphuric acid, known as basic persulphates. 

 Marcasite is much more susceptible to such changes than the cubical form. "When the 

 oxidising action takes place very slowly, so that the sulphates may be removed as they 

 are produced, pyrites may become completely changed into hydrated peroxide of iron 

 without change of form. This is commonly observed in pseudomorphous crystals of 

 pyrites, the resulting minerals containing about the same percentage of iron as the 

 original : the change takes place without any great alteration of volume. 



2. Magnetic Iron Pyrites, Pyrrhotine. This mineral crystallises in the hexagonal 

 system, and occurs chiefly in the crystalline rocks, in veins with various ores. Its 

 colour is between bronze-yellow and copper-red, with a pinchbeck-brown tarnish ; 

 streak greyish-black ; it is more or less magnetic. When heated in an open tube it 

 yields sulphurous acid fumes, but no sublimate ; before the blowpipe on charcoal in 

 the reducing flame it fuses to a black strongly-magnetic globule ; it is soluble in 

 hydrochloric acid, evolving sulphuretted hydrogen and depositing sulphur. According 

 to G. Rose, this mineral always contains a larger proportion of sulphur than corresponds 

 with the simple sulphide FeS ; and he adopts for it the formula 5FeS + Fe 2 S 8 ; corre- 

 sponding with 60-44 iron and 39'56 sulphur, which agrees very closely with the 

 analyses that have been made by Stromeyer, H. Eose, and others. 



3. Mispickel ; Arsenical Iron; Arsenikkies. This mineral crystallises in the 

 rhombic system, and is also found massive, granular, or columnar, and disseminated. 

 It is brittle, with an uneven fracture ; colour, silver-white, or almost steel-grey, with 

 a greyish or yellowish tarnish ; specific gravity 6 to 6'2. When heated in a closed 

 tube it yields first a red, then a brown sublimate of sulphide of arsenic, and then 

 metallic arsenic. Some varieties contain silver or gold, in others part of the iron is 

 replaced by cobalt or nickel. Viewing it as a double sulphide and arsenide of iron, 

 its formula would be FeS z + FeAs, which requires iron, 33'5 ; sulphur, 19 - 9; arsenic, 

 46'6. A specimen analysed by Plattner gave iron, 34-46; sulphur, 20'07 ; arsenic, 

 45-46. Mispickel is common in the mines of Freiberg in Saxony, and in the tin mines 

 of Bohemia, Silesia, and in Cornwall. It is of no use as an ore of iron, but it is 

 occasionally worked for the silver it contains, and as an ore of arsenic. 



4. Lolingite, or Leucopyrite ; Glanzarsenikkies ; Arseneisen, Mohsine ; contains iron, 

 sulphur, and arsenic. It occurs at Reichenstein in Silesia, in serpentine, and is prin- 

 cipally of interest from having been the first mineral from which gold was extracted 

 by Plattner's process of acting on the burnt residues after the' removal of arsenic with 

 chlorine gas. (See CHLOHINATION.) Dana gives the following analyses of Lolingite : 



Arsenic Sulphur Iron Nickel Cobalt 



Reichenstein 65'99 1'94 28'06 ... ... Hoffmann 



Fossinn 70'09 1-33 27'39 ... ... Scheerer 



Schladming 60'41 5-20 13-49 13-37 5'10 Hoffmann 



The name leucopyrite is derived from \tvic6s, leukos, white, and pyrites ; it was given 

 to the species by Shepard in 1835, antedating Haidinger's Lolingite and Chapman's 

 Mohsine. 



5. Copper Pyrites, Chalcopyrite, Yellow Copper Ore. The common copper ore of 

 Cornwall. It appears to be a double sulphide of copper and iron ; its composition 

 being, sulphur, 34'9 ; copper, 34'6 ; iron, 30'5. See COPPER. 



6. "Pin Pyrites, Sulphide of Tin ; Bell-metal Ore. This mineral is found in many 

 of the Cornish mines. Its composition is sulphur, 30'0 ; tin, 27'2 ; copper, 297 ; 

 iron, 13-1. 



The production of iron pyrites in the United Kingdom in 1872 and 1873 is shown 

 at top of next page. 



Imports of Pyrites of Iron, Copper, or Sulphur, in 1874. 

 500,831 tons; value 1,259,9852. 



Iron pyrites, or mundic, is a mineral which is largely employed in the manufacture 

 of copperas and of sulphuric acid. The pyrites (' brasses ') of the Coal-measures are 

 used in the preparation of copperas. Mr. Kirwan, in his ' Mineralogy,' gives us the 

 following passage, which shows that the changes which take place in the sulphur 

 ores (Martial Pyrites) had been well studied by him : 



' Vitriol is formed in these stones by exposing them a long time to the action of the 

 air and moisture, or by torrefaction in open air, and subsequent exposure to its action, 

 which operation in some cases must be often repeated, according to the proportion of 



