532 SYSTEMATIC DESCRIPTION OE PRECIOUS STONES 



IRON PYRITES. 



Iron -pyrites, or simply pyrites, is often known to jewellers as marcasite, though by this 

 term mineralogists refer to another species. It is disulphide of iron, its composition being 

 represented by the formula EeS^, and is the only mineral sulphide with a metallic lustre 

 which is used for ornamental purposes. It crystallises in the cubic system, has a specific 

 gravity of 5'0, and a hardness (H = 6i) a little less than that of quartz. The mineral is brittle, 

 and when heated before the blowpipe it burns with a bine flame and gives off sulphur dioxide, 

 easily recognised by its penetrating odour. When struck with a steel, iron-pyrites gives out 

 brilliant sparks and a smell of sulphur dioxide, due to the ignition of the particles struck off. 

 It is unattacked by hydrochloric acid, but completely decomposed by nitric acid. 



This mineral is of a pale brass-yellow colour and possesses a brilliant metallic lustre, 

 well shown in cut stones, which are usually given the form of a flat rosette. On account 

 of the comparative hardness of the stone the lustre is retained for a long time, and the edges 

 of a cut stone do not very soon lose their sharpness. 



Up to the eighteenth century iron-pyrites was much esteemed, especially in France, as 

 an ornamental stone on account of its brilliant lustre and pretty colour ; it was used for the 

 decoration of shoe-buckles, garters, snuff-boxes, &c., besides being set in brooches, bracelets, 

 and other articles of personal ornament. Afterwards the mineral grew more and more out 

 of favour until its use was practically given up. Attempts have been made to reinstate it in 

 its former position ; thus in the year 1846 a large amount of iron-pyrites, from Geneva and 

 the Jura Mountains, set in an old-world and once admired fashion, was sent to Paris. The 

 articles were readily bought up at first, but being dear and the setting not in accordance 

 with the taste of the period there was no sustained demand for them. There is sometimes 

 used in cheap jewellery at the present time a material, occurring in the neighbourhood of 

 Dublin, which consists of a thin incrustation of small and brilliant crystals of iron-pyrites on 

 the surface of black shales of Carboniferous age. Large polished plates of iron-pyrites, 

 which were probably used as miiTors, have been found in the ancient gi-aves of the Incas. 

 These discoveries first drew attention to the mineral, which was known for a time as 

 Inca-stone. In reference to its supposed health-giving properties it was also known as 

 health-stone, and was much worn in the shape of amulets, as well as set in necklaces, pins, 

 ear-rings, &c., and was possessed of considerable value. Iron -pyrites exists in nature in very 

 great abundance, and is one of the most widely distributed constituents of the earth's 

 crust. 



