| Mesitite | |
|---|---|
 Mesitite from Traversella (Piedmont) | |
| General | |
| Category | Carbonate mineral |
| Formula (repeating unit) | (Mg,Fe)CO3 |
| Crystal system | Trigonal |
| Identification | |
| Color | from whitish, gray or yellowish to gray-brown or brown |
| Cleavage | perfect on a rhombohedron |
| Mohs scale hardness | 4.0-4.5 |
| Luster | glassy or pearlescent |
| Diaphaneity | translucent to opaque |
| Density | 3.0-3.6 (calculated) |
Mesitite (from Ancient Greek: μεσιτης — middle, between), formerly better known as Mesitine spar, Ferrous magnesite ou Brown spar (German: braunspat) is a * variety of magnesite, a carbonate mineral, one of the so-called brown spars, regarded as an iron-bearing variety of magnesite or, in other cases, breunnerite. True to its name, mesitite is the middle member of a continuous isomorphic series magnesite → siderite with the general formula (Mg,Fe)CO3, in which the iron ion content (Fe) is approximately 30 to 50%, and the iron to magnesium ratio is, accordingly, from 30:70 to 50:50..
Name and history
Mesitine spar, later abbreviated mesitite — in accordance with the internationally accepted terminology mesitite, less commonly mesitin (from German: mesitinspath) was an old trivial name, widely used among miners, geologists and mineralogists for some ferruginous magnesites. Until the end of the 19th century, various authors sometimes considered mesitine spar to be a synonym (variety) of breunnerite, in other cases — a synonym (variety) of pistomesite. In the most general form, mesitine was considered to be a brown spar, which in turn is a variety of bitter spar (in this case, more often magnesite), colored with manganese or iron carbonate.
The name itself simultaneously defined both the proportions of chemical compounds in its composition and the position of the mineral among related spars (the Greek word μεσιτης — means middle, located in the middle). For example, in 1835, Vladimir Eremeev′s German-Russian dictionary of technical terms and names defined mesitine spar as «forming a middle ground between brown spar and sparous iron ore». Although the definition of brown spar itself was broad, it concerned several different minerals and was not very clear.
Definitions in English mineralogy were distinguished by approximately the same precision. In particular, in 1853, James Dwight Dana described this mineral in his «Manual of Mineralogy″ with the following words: «Mesitine spar. (Breunnerite). A carbonate of iron and manganese, occurring in yellowish rhombohedrons of 107°14′. <...> This includes much of what is called rhomb spar, or brown spar, which becomes rusty on exposure.»
Alexander Ramsay′s definition, given a decade and a half later, turned out to be much more accurate: «This species is composed of spathic iron ore, or chalybite and magnesite, frequently in equal proportions. The crystals are rhombohedrons, with a terminal angle of 107°14′, having a grey or yellowish colour, a vitreous and slightly pearly lustre; a hardness of 4 to 4.5; a specific gravity of 3 (33,434) to 3.6 (40,140), and a transparency somewhat greater than that of chalybite. It is found in chlorite slate at St. Gothard, also in the Zillerthal, in the Tyrol, and in Piedmont».
Mineralogy of the 20th century came to define mesitite as the middle (median) member of a continuous isomorphic series of ferruginous magnesites (magnetite → siderite) with the general formula (Mg,Fe)CO3, located in the middle in composition between breunnerite and pistomesite. Depending on the content of the FeCO3 molecule, four varieties are distinguished in this series. The first is breunnerite, in which the iron content is the lowest (up to 30%), and the properties are closest to magnesite; then comes mesitite, containing up to half of siderite (30-50% FeCO3); the iron content is even higher in pistomesites (50-70% FeCO3) and the last, closely adjacent to iron spar, is sideroplesite (70-95% FeCO3).
Properties
In the 19th century, mesitin spar was often considered a variety of breunnerite, at that time the best known of the ferruginous magnesites. Likewise, in the first half of the 20th century, breunnerite remained the best known of all varieties, but it, too, never had the status of an independent mineral species.
In terms of composition, mesitine spar (included in an indefinite number of breunnerites) was represented as an isomorphic mixture of magnesia carbonate (magnesite) and iron carbonate (siderite) in various proportions; or MgCO3, with an admixture of FeCO3. For example, Dmitri Mendeleev in his master's thesis «Isomorphism in Connection with Other Relationships of Crystal Form to Composition» recommended depicting the formula of mesitine spar as (½Fe•½Mg)C or simply (MgFe)C. Another graphical version of the formula of mesitine spar was considered to be (Mg:FeO)CO2.
The Soviet school of mineralogy often continued to traditionally classify the above-mentioned sideroplesite (70 to 95% FeCO3), pistomesite and mesitite as varieties of breunnerite, nevertheless stipulating that “...breunnerite itself, the most common in nature, refers to varieties with a FeCO3 content of up to 30%.”
In the early 1950s, luminescence studies were conducted in Moscow in trigonal carbonates formed by mixed crystals of CaCO3 — MgCO3 (dolomite) with subsequent isovalent substitution of magnesium by iron, manganese, and sometimes zinc. Within the indicated isomorphic series, many mineral species and varieties were studied, revealing some regular changes in luminescent properties. Among the general properties, it was first revealed that iron impurity, present in the form of FeCO3 in mixed crystals, such as breunnerite (MgFe)CO3, or isovalently substituting magnesium ions, causes a hard quenching effect. None of the studied minerals (breunnerite, ankerite, mesitite, including, of course, siderite) gave a luminescent effect in any of the types of radiation used.
Deposits
Mesitine spars are among the most widespread carbonate minerals, which is determined primarily by their composition. They have been found in all magnesite (carbonate) deposits that contain iron minerals (siderites) in one way or another. Traversella (Piedmont) has been considered the typical region from which reference samples of mesitine came since the beginning of the 19th century. In Russia, excellent museum samples of mesitine spar were found on the Nagolny Ridge (part of Donetsk), as well as in the Nerchinsk District. One of the active mesitite deposits is located in the Magadan Region.
The largest number of modern mines with established mesitites are located in Western Australia and Austria (Carinthia, Salzburg, Tyrol). In France, mesitite spars are known from the northeastern deposits of the Grand Est province, as well as in Occitania and the Provence-Alpes region.
See also
References
- ^ Mesitine Spar, a variety of Magnesite: information about the mineral Mesitine Spar in the database Mindat.
- Mesitite, a synonym of Mesitine Spar: information about the mineral Mesitite in the database Mindat.
- ^ A. G. Betechtin, Mineralogy. - Moscow: Gosgeolizdat, 1950. — 957 p.
- ^ Dana, James Dwight (1853). Manual of Mineralogy: Including Observations on Mines, Rocks, Reduction of Ores and the Application of the Science to the Arts. — Durrie and Peck (5th edition), 1853.
- ^ Alexander Ramsay, Jun. The Rudiments of Mineralogy; a Concise View of the General Properties of Minerals. — London: Virtue & Co., 26, Ivi Lane. 1868.
- James Apjohn. A descriptive catalogue of the simple minerals in the systematic collection of Trinity College, Dublin Dublin: Printed by M.H. Gill, 1850.
- V. P. Eremeev. German-Russian dictionary of technical terms and names used in: geognosy, geology, mining art... etc., with an explanation of the real meaning of many words taken from other languages and especially from Greek. — Saint Petersburg: type. Medical dep. of the Ministry of Internal Affairs, 1835. — 169 p. (in Russian)
- Karpinsky A. P. Collected Works. Volume Three. — Moscow, Leningrad: Publishing House of the USSR Academy of Sciences. 1939.
- D. I. Mendeleev. Works: in 25 volumes. Volume 1. — Leningrad: Chim-teorete, 1954-1959.
- G.P.Barsanov, V.A.Sheveleva. Materials on the study of mineral luminescence. II. Carbonates. — Moscow: Proceedings of the Mineralogical Museum, Volume 5, 1953.
- Brief catalogue of the mineralogical collection of the Mining Institute Museum. Compiled by Lieutenant Colonel V.V.Nefedyev. — St. Petersburg: Printing House G. Schroeder, 1871. — 588 p.
External links
- Mesitine Spar, a variety of Magnesite: information about the mineral Mesitine Spar in the database Mindat.
- Mesitite, a synonym of Mesitine Spar: information about the mineral Mesitite in the database Mindat.
- Magnesite var. Mesitite (Traversella, Torino Province, Piedmont): Robertson Coll.