Aerinite

Aërinit

The mineral Aerinit (also Aërinit ) is a rarely occurring chain silicate mineral from the class of " silicates and Germanates ". It crystallizes in the trigonal crystal system with the chemical composition ( Ca 5, 1Na0, 5) ( Fe3 AlFe2 1.7 Mg0, 3) ( Al5, 1MG0, 7) [ Si12O36 (OH ) 12H ] · [ (CO3) 1.2 ( H2O ) 12] and usually develops massive aggregates and crusty coatings, rare small, fibrous crystals in sky-blue to blue- green color with blue white stripe color.

Special Features

Aerinit one of the pigments and is, for example, able than inclusion (inclusion ) in quartz this bluish color.

Etymology and history

The word is derived from the Greek Aerinit ἀέρινος aerinos for sky blue in reference to its color.

Aerinit was first discovered in Caserras del Castillo in the Spanish community Estopiñán del Castillo and described in 1876 by Arnold von Lasaulx, which struck the mineral in the built-up from its predecessor Martin Websky mineralogical collection of the University of Breslau, due to its vibrant blue color. When he examined the mineral identified as " Vivianit from Spain " closer, he noted that, in contrast to this was phosphoric free. Further investigation eventually made ​​it clear that it was a new, previously unknown mineral in the mineral sample from Spain.

The originally selected by Lasaulx spelling Aërinit has been discredited since 2008, as it is in the double dot over the 'e' ( Trema ) a, the word origin is to unnecessary diacritical mark.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Aerinit belonged to the mineral class of " silicates and Germanates " and then to the Department of " chain silicates and phyllosilicates ( inosilicates ) ", where he formed a distinct group with Alamosit.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Aerinit also in the class of " silicate and germanate " and there in the department of " chains and chain silicates ( inosilicates ) " one. This division, however, is further divided according to the structure of the chains, so that the mineral according to its construction in the subsection " chain and chain silicates with 2- periodic single chains Si2O6; with additional O, OH, H2O to find related pyroxene minerals ", where the only member is the unnamed group 9.DB.45.

The classification of minerals according to Dana assigns the Aerinit in the class of " silicates and Germanates " there, however in the fine already divided the department " chain silicates: structures with chains of different width". Here is the mineral as the only member of the unnamed group 68.01.03 within the subdivision: to find " chain silicates structures with chains of different width".

Education and Locations

Aerinit be hydrothermally formed at relatively low temperature, among others, in the zeolite facies. Accompanying minerals include prehnite, Skolezit and Mesolith.

Worldwide, Aerinit so far (as of 2011) are detected in fewer than 20 archaeological sites. Apart from its type locality Estopiñán del Castillo ( Aragón ), the mineral in Spain was still in Olvera and Antequera in Andalusia, in Tartareu in the Catalan municipality Les Avellanes i Santa Linya ( Lleida province ) and in Albatera, Los Serranos, Los Vives (near Orihuela, Alicante) and Los Arenales Province (Castellón ) in Valencia province be found.

Other localities are Saint- Pandelon in the French Department Landes and Millington in the U.S. Bernards Township (New Jersey).

Crystal structure

Aerinit trigonal crystallized in the space group P3c1 ( Raumgruppen-Nr. 158) with the lattice parameters a = 16.87 Å and c = 5.23 Å, and one formula unit per unit cell.

The crystal structure is interesting in two respects. On the one hand Aerinit one of the few chain silicates, install the CO3 as integral part of their structure ( Caysichit - (Y), Ashcroftin - (Y), Fukalith the others). On the other hand contains Aerinit face-sharing FeO octahedra, in which the Fe cations are unusually close.

The Si4 cations are surrounded by 4 oxygens tetrahedrally. This SiO4 tetrahedra are too simple chains connected with the periodicity 2 as in pyroxenes than 2 oxygens. The chains run parallel to the crystallographic c -axis.

Al3 and Mg2 are of 2O2 and four OH - groups surrounded octahedrally. These octahedra are linked via 2 common edges to zigzag chains extending along the c- axis kristatallographischen.

The Fe2 and Fe3 cations are octahedrally surrounded by six oxygens. These octahedra are connected by two surfaces in the direction of c-axis to form chains. In the chain neighboring Fe cations of different charge exchange through the shared octahedral face from her Koordinationdpolyeder electrons and form a delokalisertes electron system on the Fe - cations of octahedra. This absorbed light in the yellow wavelength range and thus colors the Aerinit blue. The orientation of the face-sharing octahedra, and thus the Fe - Fe delocalized electron system is parallel to the c - axis direction is responsible for the strong dependence of the color of the Aerinit ( pleochroism ).

Fe octahedra each is connected to three Si Tertaederketten, wherein the oxygen atoms are at the corners of Fe octahedra are also the tips of the tetrahedra of the silicate coordination chains.

Each 6 silicate tetrahedral chains are about 6 Al- octahedra connected to large, 12-sided channels that run through the Aerinitstruktur parallel to the c axis. Sit the Ca2 cations, forming the center of the channel towards weak ionic bonds with the oxygens of two H2O molecules at the Al octahedra on the inside of the channels. In the center of the channels, the planar CO3 groups lie with their plane perpendicular to the c axis. The oxygen of the CO3- groups are connected to form strong hydrogen bonds with H2O three molecules, which are in turn connected via the Ca2 ions with the inner wall of the channels.

Each of H 2 O CO3- channels is connected to the Al- octahedra with 6 additional H2O CO3 channels and the silicate tetrahedrons chains with 6 Fe octahedra.

Use

Aerinit found due to its intense color regionally limited use as a blue pigment for wall paintings. Typical is the use of Aerinit for religious frescoes in northern Spain ( Catalonia, Aragon ) and Albania during the Middle Ages ( 11-16 century). He gives the murals of the Catalan Romanesque their characteristic blue and green tones.

Outside of northern Spain was the use of Aerinit be detected only for medieval frescoes in two places in France ( Abbey of Moissac, 12 century collegiate church of Saint -Nicolas, Nogaro, 11 century). This is gewerted as Indiez for the exchange of artists and material over the Pyrenees across during the Middle Ages.