Tranquillityite

• IMA 1971-013

Tranquillityit is a very rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the hexagonal crystal system with the composition Fe82 Ti3 (Zr, Y ) 2 [ O12 | (SiO4 ) 3], and is therefore chemically seen island silicate with oxygen as additional anions and iron, titanium and zirconium or smaller proportions of yttrium, the the zirconium may replace diadoch.

Special Features

The analyzed sample contained less than 10% impurities (Y, Al, Mn, Cr, Nb, and other rare earths), and up to 0.01% (100 ppm) of uranium. This amount of uranium made ​​it possible to determine the age of Tranquillityit and several associated minerals in Apollo 11 samples by uranium-lead method with 3.71 billion years. It is believed that the predominantly amorphous structure of the metamikte Tranquillityit caused by alpha radiation from the decay of uranium.

The crystals were obtained by annealing the samples at 800 ° C for 30 minutes. The crystal quality not improved by the longer annealing, annealing at higher temperatures led to spontaneous rupture of the sample. A Tranquillityit -like crystalline phase has been synthesized by mixing oxide powders in the same ratio as in the lunar rocks and annealing the mixture at 1500 ° C. The resulting phase was not pure but interspersed with various intermetallic compounds.

Etymology and history

It is named after the Sea of ​​Tranquility ( Sea of ​​Tranquility ) on the moon, where in 1969 during the Apollo 11 mission, the rock samples were collected, in which the mineral was discovered later. It was the last mineral found on the moon, which was thought to be unique, ie without incidence on the ground until it has been found in Australia 2011.

1970 found materials scientists in the lunar rock sample No. 10047 an unknown silicate mineral containing iron, titanium and zirconium and rare earths contained. The first detailed analysis of the new mineral was published in 1971 and accepted the proposed name Tranquillityit of the International Mineralogical Association (IMA ). Later it was discovered that it is contained in the lunar rock samples of all the Apollo missions.

Classification

Already in the now outdated but still in use 8th edition of the mineral classification by Strunz was one of Tranquillityit to the mineral class of " silicates and Germanates " and then to the Department of " island silicates with tetrahedral foreign anions ( Neso - Subsilikate ) ", where he is the only member independent group VIII/B.07 formed.

The valid since 2001 and used by the IMA 9th edition of the Strunz'schen Mineral classification assigns the Tranquillityit also included in the category of " silicates and Germanates " and then in the Department of the " island silicates ( nesosilicates ) ". This division, however, is further subdivided according to the possible presence of other anions and the coordination of the cations, so that the mineral according to its composition in the subdivision of " island silicates with additional anions; Cations can be found in most cases and > coordination " where it also forms the unnamed group 9.AG.90 without further members.

The mainly common in English-speaking classification of minerals according to Dana assigns the Tranquillityit in the class of " silicates and Germanates " and there in the department of " Unclassified silicate minerals " one. Here he is the only member / along with unnamed in the group 78.07.16 within the subdivision: to find " Unclassified silicates complete unclassified silicates ".

Education and Locations

Tranquillityit formed thin, up to 15 times 65 micron wide stripes in basaltic rocks, in which it is formed at a late stage crystallization. Tranquillityit associated with troilite, Pyroxferroit, cristobalite and alkali feldspars. It is almost opaque and appears dark red - brown as a thin crystal.

How Armalcolit and Pyroxferroit Tranquillityit was found later on the earth, among others, as a fragment in the Martian meteorite NWA 856 from Northwest Africa. However, these particles do not come originally from the earth.

Only in 2011 was discovered in six locations on the Pilbara region of Western Australia original earthly occurrences of Tranquillityit. These include some Dykes and sills of diabase and gabbro, which originate from the Proterozoic to Cambrian. The Tranquillityit occurs here in the form of stored grains in Zirkonolith, baddeleyite and apatite associated with final phase intergrowths of quartz and feldspar.

Crystal structure

Tranquillityit crystallized hexagonal with lattice parameters a = 11.69 Å and c = 22.25 Å and 3 formula units per unit cell.