Mellite

• Honeystone

Mellit, also known as the honey stone, is a rarely occurring mineral from the mineral class of " organic compounds ". It crystallizes in the tetragonal crystal system with the chemical composition Al2C6 (COO ) 6 • 16H2O, is so chemically speaking, the aluminum salt of mellitic (also Aluminiummellitat or aluminum mellitate ).

Mellit usually develops Dipyramid crystals in the centimeter range with resin to glass glossy surfaces, but also granular aggregates. Pure Mellitkristalle are colorless and transparent. In multicrystalline training or lattice defects can, however, appear white due to multiple refraction and accept by foreign admixtures a honey-yellow, deep red or brown color, the transparency decreases accordingly.

With a Mohs hardness of 2 to 2.5 mellit belongs to the soft minerals that are similar as the reference mineral gypsum ( Mohs hardness 2 ) can barely scratched with a fingernail.

Special Features

Under UV light, show some Mellite a pale yellow or blue fluorescence.

Mellit is soluble in nitric acid and potassium hydroxide, but insoluble in water and ethanol. When heated to about 300 ° C, it is gradually decomposed, wherein as an intermediate is formed of the hexahydrate mellitic.

Etymology and history

Mellit was first discovered in the " brown coal mine Auguste " in Artern at the Unstrut in Thuringia.

A first brief description of the Minerals provides 1789 Christian August Siegfried Hoffmann, using Abraham Gottlob Werner's mineral system and synonym honeystone the note: "A still fairly unknown fossil, whose father is the state of Thuringia. It is honey- yellow color and is found in double four -sided pyramids kristallisirt " holds.

A more precise indication of the locality as well as various properties of the mineral supplies Dietrich Ludwig Gustav Karsten, who also in 1789 some mistakenly dispatch tickets in the review of the mineral collection of Nathanael Gottfried Leske under the gypsum samples is perfectly octahedrally grown and honey- yellow crystals. To the knowledge of Werner's new mineral system with the honey stone as well as our own studies listed there Karsten recognizes him as identical with this. In his notes, he describes the mineral under the heading of honey stone after Werner mineral system ( 95th class ) as bitumen melliadites, which is found between the bearings of the bituminous - wood of Artern. The detailed description by Karsten Werner took over in 1792 in his book " Oryktognosie or user manual for lovers of Mineralogy ".

The still valid name mellit goes back to Johann Friedrich Gmelin in 1793, written in Latin Mineral classification, the designated and the mineral as Mellites (after the original Greek word μέλι [ meli ] for honey) thereby to the descriptions of Werner and Karsten relates. Richard Kirwan walked this term in 1796 in his book " Elements of Mineralogy " in Mellilite from that will eventually shortened in 1801 by René -Just Haiiy on mellit ( Mellite ).

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the mellit belonged to the mineral class of " organic compounds " and then to the Department of " salts of organic acids ," where he along with Julienit and the other members Abelsonit, Calclacit, Dashkovait, Earlandit, Formicait, Hoganit, Kafehydrocyanit and Paceit the independent " mellit - Julienit group" was formed.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the mellit in the category of " organic compounds " and there in the department of " salts of organic acids " a. This division, however, is further subdivided according to the salt-forming acid, so that the mineral is found according to its composition in the subsection " benzene salts" where it only forms the unnamed group 10.AC.05 together with Pigotit.

The mainly common in English-speaking classification of minerals according to Dana assigns the mellit into the class of " Organic Minerals " and then in the same department. Here he is the only member of the unnamed group 50.02.01 within the sub-division of " salts of organic acids ( mellitates, citrates, cyanates and acetates ) " to find.

Education and Locations

Mellit is a rare secondary mineral and is grown up, in small groups or Druze in brown coal, rare in coal and sandstone.

So far, the mineral could only at a few localities demonstrated ( number of registered localities in mindat.org around 10 ). Apart from its type locality Artern at the Unrut in Thuringia occurred in Germany nor in the former brown coal mining on at Goitzsche in Saxony -Anhalt.

Noteworthy due to exceptional Mellitfunde is among other things the " Csordakúti Mine" at Bicske and the coal mines at Tatabánya in Hungary, where crystals up to 4 cm in size were revealed. From Valchov ( Moravia), the Czech Republic is rather grainy aggragate come, but we know from the Czech Bohemia beautiful crystal finds.

In Austria mellit was previously only Lanz - Stelzling found in the market town Kötschach -Mauthen in Carinthia. Other localities lie near Paris in France and in Bogorodizk ( Bogorodetsk ) in the Russian Tula Oblast ( Tulskaya ).

Synthetic production

The mellitic ( benzenehexacarboxylic ) C12H6O12 can be shown from the honey stone deposited and also by treatment of coal with potassium permanganate in alkaline solution; it forms colorless needles, is readily soluble in water and alcohol, taste and strong acid reaction and decomposes when heated with excess lime in carbonic acid and benzene.

Crystal structure

Mellit crystallized tetragonal in the space group I41/acd ( Raumgruppen-Nr. 142) with the lattice parameters a = 15.55 Å and c = 23.21 Å, and eight formula units per unit cell.

Use

Mellit has except as a mineral sample of no economic importance. Occasionally he is but honed by experienced hobby grinders for collectors and enthusiasts to gemstones.