Gehlenite

Gehlenite is a rarely occurring mineral from the mineral class of " Silicate and germanate ". It crystallizes in the tetragonal crystal system with the chemical composition Ca2Al [ AlSiO7 ] and usually develops transparent to translucent crystals of dicktafeligem or short prismatic habit and white, gray or yellowish color, but also granular to massive mineral aggregates.

Gehlenite forms with akermanite a perfect mixed batch.

Etymology and history

Was first found in 1815 at Monte Gehlenite Monzoni in Val di Fassa in Italy and described by Johann Nepomuk Fuchs, who named the mineral after the German chemist Adolf Ferdinand Gehlen, the type locality is situated in the Val di Fassa in the province of Trento, Italy.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the gehlenite belonged to the mineral class of " silicates and Germanates " and then to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

The 9th edition used since 2001 and valid by the International Mineralogical Association (IMA ) of the Strunz'schen Mineral classification assigns the gehlenite 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 together with akermanite, Barylith, Cebollit, Gugiait, hardystonite, Jeffreyit, melilite and Okayamalith the " in tetrahedral and higher coordination melilite group "with the system no. 9.BB.10 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the gehlenite 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. Here he is with akermanite, melilite and Okayamalith in the " melilite group " with the system no. 55.04.01 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

Gehlenite can occur naturally in plutonic rocks, metamorphic rocks and meteorites or artificially by high tempered firing carbonate - hältiger ceramics. High-temperature metamorphism of " unclean " ( alumino silicate containing ) limestones or contact metamorphism of igneous rocks with carbonates can lead to the formation of gehlenite. The mineral has also been described in chondritic meteorites and is considered as a condensation product of the pre-solar nebula.

Worldwide, gehlenite so far (as of 2010) are detected in about 60 localities, as in China, Germany, Iran, Israel, Italy, Japan, Mexico, New Zealand, Austria, Romania, Russia, Sweden, Czech Republic, Uganda, Hungary, the United Kingdom ( UK), and in the United States (U.S.). Also in the comet dust from Wild 2 Gehlenite could be detected.

Crystal structure

Gehlenite crystallized tetragonal in the space group P421m with the lattice parameters a = 7.69 Å and c = 5.07 Å and two formula units per unit cell.

The construction of the crystal structure is carried out by groups of layer -like ( 100) is arranged [ AlSiO7 ] - and [ AlO4 ] tetrahedra, which are linked by Ca -O- bonds, Ca to O occurs in coordination.

Use

Since gehlenite is relatively easy to detect due to its good crystallinity by X-ray diffraction and under atmospheric pressure conditions has a very limited education or stability field, this mineral can be very well used for the determination of firing temperatures of ancient pottery. This " thermometer ", however, can only be used in carbonate ceramics as an adequate amount of reactive calcium must be available for the reaction of formation of gehlenite.