A Stone Sulphuric Acid Is Made Of
When exposed to air, this stone turns dark; neither it is resistant to moisture attack. Both the downsides did not, however, stop the mineral from turning into a sought-after analogue of diamonds.
Before the start of the 19th century, marcasite was often mistaken for another mineral - pyrite. And in France, for example, pyrite jewellery was sold under the trade name 'marcasitae'. The similarity between the two minerals manifests itself even through the second name of marcasite - 'white iron pyrite'. But despite the common features - similar colour, commonalities in structure, - they still physically and crystallographically differ. An Austrian mineralogist defined the differences between the two stones and proposed separate names to each of them. Yet even two centuries later, the confusion is far from being over. Marcasite jewellery, contrary to the scientific sense, is actually made from pyrite, not from the mineral marcasite.
The use of the mineral in imitating diamonds dates back to the reign of Louis XIV, King of France. At the time wearing jewels with diamonds was heavily regulated by court etiquette. As one of the rules demanded, only married ladies could put items of diamond jewellery on them. Besides, it was not allowed to wear jewels with the gem in the daytime but only within the fixed evening hours. Therefore, silver items with marcasite inclusions served as a reasonable alternative for nobles who wanted to abide by the rules. The stone of tin-white colour was similar in beauty to diamonds but was much cheaper.
Naturally occurring samples are rather unattractive in its outward appearance. The stone's beauty does not reveal itself until after processing. The problem is that marcasite is a brittle material, thereby it was mainly cut into small, round-shaped rock pieces. Those were mounted then into items of silver, thus increasing the products' metallic lustre manifold.
The mineral fast disintegrates if exposed to moisture, becomes opaque and darkens in air, often crumbles and breaks even at slight physical impact. Despite what is mentioned above, it still remained a popular jewellery material, valued, for instance, by Maria Feodorovna, Empress consort of Russia. The wife of Emperor Alexander III was fond of her marcasite collection, believing the jewels brought her luck.
Use of marcasite as a gem soon ceased due to its brittleness. Thereupon marcasite jewellery became an extreme rarity. If still working with the stone, the highest qualification is required. Accordingly, all marcasite products arouse the genuine interest of collectors.
If one wants to preserve a mineral sample in their collection intact, it must undergo specific processing first. Otherwise, the specimen quickly loses its lustre. One of the most valuable varieties of marcasite is iridescent spectropyrite.
There is a practical application of marcasite. In the past, it was used as an additive to cement, to improve its hardness. Low stone's durability under exposure to air, however, prevents such use for safety reasons. Nowadays, marcasite is used to produce sulphuric acid, for which is high demand in the petroleum and metal industries. There is also use for sulphuric acid in the extraction of such rare elements as uranium.
Sulphuric acid is most often produced via the contact process, consisting of several steps. At first, the sulphur-bearing mineral is crushed to small pieces, and then it is burned to produce sulphur dioxide. The latter is, in turn, is oxidised, and, with the presence of water, sulphuric acid is formed.
Due to being sulphide mineral, marcasite if heated generates a flame of blueish colour with a typical odour.