Pigeonite

Pigeonite is a rarely occurring mineral from the mineral class of " silicates and Germanates ". It crystallizes in the monoclinic crystal system with the chemical composition (Mg, Fe, Ca ) 2 [ Si2O6 ] and developed prismatic, up to a centimeter wide, translucent crystals of gray-brown, greenish or black color.

Etymology and history

Was first discovered Pigeonite at Pigeon Point in the State of Montana and described in 1900 by Alexander Newton Winchell, who named the mineral after its type locality.

Classification

In the now outdated but still in use 8th edition of the mineral classification by Strunz the Pigeonite belonged to the mineral class of " silicates and Germanates " and then to the Department of " chains and chain silicates ( inosilicates ) ", where he, together with aegirine, augite, diopside, Esseneit, hedenbergite, jadeite, Jervisit, Johannsenite, Kanoit, Klinoenstatit, Klinoferrosilit, Kosmochlor, Namansilit, Natalyit, omphacite, Petedunnit spodumene and the subset of " clinopyroxene " with the system no. VIII/F.01 formed within the pyroxene group.

The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the pigeonite also in the class of " silicates and Germanates " and there in the department of " chains and chain silicates ( inosilicates ) " one. This division, however, is further subdivided according to the type of chain formation and membership of larger mineral families, so that the mineral in accordance with the subdivision " chain and chain silicates with 2- periodic single chains Si2O6; Pyroxene family " is to find where it together with Klinoenstatit, Klinoferrosilit, Halagurit and Kanoit the " Mg, Fe, Mn clinopyroxene, Klinoenstatitgruppe "with the system no. 9.DA.10 forms.

The mainly common in English-speaking classification of minerals according to Dana assigns the pigeonite in the class of " silicates and Germanates " and there in the department of " chain silicate minerals " one. Here he is with Klinoenstatit, Klinoferrosilit and Kanoit in the group of "P2 / c clinopyroxene " with the systen no. 65.01.01 within the sub-division of " chain silicates: Simple unbranched chains, W = 1 with chains P = 2" to find.

Education and Locations

Pigeonite forms in highly heated mafic rocks such as basalt, which are rapidly cooled. At the same time only small amounts of calcium may be present for the formation, otherwise the similar mineral augite occurs. Typically this is the case in some volcanoes. In addition to these it is also found in meteorites that have fallen to the ground.

A typical example of a volcano, pigeonite formed during the eruptions of the Soufriere Hills is on the Caribbean island of Montserrat and an example of a meteorite find is the Cassigny meteorite in France.

Overall pigeonite has so far (as of 2011) are detected in over 120 localities. Apart from its type locality Pigeon Point the mineral still occurred in the United States at several places in the states of Alabama, Arizona, Maine, Massachusetts, Michigan, Nevada, New Mexico, Pennsylvania and Virginia, and in the San Juan Mountains in Colorado, at Red Oak in Fulton County ( Georgia), Lafayette ( Indiana), in Gray County ( Kansas ) in Beaver Bay, Minnesota, in Stillwater County ( Montana), in Moore County ( North Carolina), at Shrewsbury in Rutland County (Vermont ), in Washougal in Washington and on the Potato River in Ashland County ( Wisconsin).

In Germany you will find Pigeonite among others Roehrnbach in the Bavarian Forest, near Bad Harzburg in Lower Saxony Harz and in Rockeskyll volcanic complex in the Rhineland-Palatinate Eifel.

Other localities are Algeria, Antarctica, Australia, Brazil, China, Greenland, India, Cogne in Italy, Japan, Yemen, Libya, Morocco, Whangarei in New Zealand, Oman, Papua New Guinea, Romania, Russia, Sweden, Slovakia, Spain, St. Lucia, South Africa, South Korea, Stonařov in the Czech Republic, Hungary, Uzbekistan and the United Kingdom ( UK).

Even in rock samples from the moon, or more precisely near the landing site of Luna 16 mission to Mare in the Moon Meteorite NWA Fecunditatis and 773 from Dchira (Western Sahara) pigeonite could be detected.

Crystal structure

Pigeonite crystallizes in the monoclinic crystal system, space group P21 / c ( Raumgruppen-Nr. 14), the lattice parameters a = 9.71 Å, b = 8.95 Å, c = 5.25 Å and β = 108.6 °, and four formula units per unit cell.

Above 950 ° C the structure goes through a phase transition into a likewise monoclinic structure with space group C2 / c.