Whilst pyrites is found abundantly in the older crystalline rocks and slates, marcasite is more abundant in clays, and has often been formed as a concretion around organic remains.
Many experiments have been made with a view to determining the difference in chemical constitution of marcasite and pyrites, but with no very definite results.
Apart from crystalline form, the external characters of marcasite are very similar to those of pyrites, and when distinct crystals are not available the two species cannot always be easily distinguished.
It is a noteworthy fact that whilst pyrites has been prepared artificially, marcasite has not.
The colour is usually pale bronze-yellow, often rather lighter than that of pyrites; on freshly fractured surfaces of pure marcasite the colour is tin-white, but this rapidly tarnishes on exposure to air.
Marcasite readily oxidizes on exposure to moist air, with the production of sulphuric acid and a white fibrous efflorescence of ferrous sulphate, and in course of time specimens in collections often became completely disintegrated.
In the Chalk of the south-east of England nodules of marcasite with a fibrous radiated structure are abundant, and in the Chalk Marl between Dover and Folkestone fine twinned groups of "spear pyrites" are common.
Marcasite is thus the less stable of the two modifications of iron disulphide.
Even when only a small proportion of mundic, pyrite or marcasite is present, it is highly objectionable for several reasons.
The opinion which some have entertained, that these mirrors were cast, has no other foundation than the likeness of polished marcasite to cast brass.
This mineral is very proper for reflecting images; and I am inclined to think that the Peruvians had better mirrors than the Greeks or the Romans, among whom we find no traces of marcasite being employed in that manner.
Pyriten argenteum was either marcasite or mispickel, neither of which offers much suggestion; nor are we able to hazard an explanation of value.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "marcasite" in a variety of sentences. We hope that you will now be able to make sentences using this word. Other words: alabaster; asphalt; mineral
