Melilite

Melilite is a rarely occurring mineral from the mineral class of " silicate and germanate ". It crystallizes in the tetragonal crystal system having a chemical composition (Ca, Na) 2 (Mg, Al) [ Si2O7 ], and usually develops only small crystals in the millimeter range with tabular or short to langsäuligem habit, but also granular to bulky mineral aggregates.

Special Features

Reiner melilite is colorless. Mostly, however, it appears by foreign admixtures of white to gray, yellow or greenish brown color.

Before the blowpipe melilite is difficult to melt. Acids destroy him, however, said he is " gelatinized ".

Etymology and history

Was discovered First melilite 1796 at Capo di Bove in the Alban hills in Italy and described by Jean -Claude Delamétherie, the meli the mineral with respect to its often honey-yellow color after the greek words for " honey " and lithos for " stone " notified.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the melilite belonged to the mineral class of " silicates and Germanates " and then to the Department of " group silicates ( Sorosilikate ) ", where he was named the " melilite group " with System no. Formed VIII/C.02 and the other members akermanite, Andrémeyerit, Barylith, gehlenite, Gugiait, hardystonite, Jeffreyit, Kaliobarylith, Meliphan and Okayamalith.

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the melilite also included in the category of " silicates and Germanates " and there in the department of " group silicates ( Sorosilikate ) ". This division, however, is further subdivided according to the nature of the silicate group formation, the possible presence of other anions and the coordination of the cations, so that the mineral according to its composition and its construction in the subsection " Si2O7 groups without non- tetrahedral anions; Cations " is to find where it is also named as the " in tetrahedral and higher coordination melilite group "with the system no. Forms 9.BB.10 and the other members akermanite, Barylith, Cebollit, gehlenite, Gugiait, hardystonite, Jeffreyit and Okayamalith.

The mainly common in English-speaking classification of minerals according to Dana assigns the melilite in the class of " silicates and Germanates " there, however, in the already fine divided department of " group silicates: Si2O7 groups, generally without additional anions " one. Again, he is a namesake of the " melilite group " with the system no. 55.04.01 and the other members akermanite, gehlenite and Okayamalith within the sub-division of " group silicates: Si2O7 groups, generally without additional anions and cations in and with lower coordination " to find.

Education and Locations

Melilite often forms as Gemengteil in ultrabasic, calcium-rich volcanic rocks, where it occurs very often in paragenesis with perovskite.

Worldwide, melilite so far (as of 2010) are detected in 130 localities, including, inter alia in Algeria, Antarctica, Bolivia, Brazil, China, Germany, France, Greenland, Israel, Italy, Yemen, Canada, Kazakhstan, the Democratic Republic of Congo, Madagascar, Mexico, Morocco, Namibia, Norway, Austria, Romania, Russia, Sweden, Switzerland, Tanzania, the Czech Republic, the USA, the United Kingdom ( UK) and in the West Bank ( Palestinian Territories ).

Melilite is also a common ingredient of so-called CAIs (calcium - aluminum - rich inclusions ) in meteorites, which are among the oldest materials in our solar system.

Crystal structure

Melilite crystallized tetragonal in the space group P421m with the lattice parameters a = 7.83 Å and c = 5.00 Å and two formula units per unit cell.