Pigeonite
| Pigeonite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | (Mg, Fe, Ca) 2 [Si 2 O 6 ] |
|
Mineral class (and possibly department) |
Silicates and germanates - chain silicates and band silicates |
|
System no. to Strunz and to Dana |
9.DA.10 ( 8th edition : VIII / F.01) 65.01.01.04 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | P 2 1 / c (No. 14) |
| Lattice parameters |
a = 9.71 Å ; b = 8.95 Å; c = 5.25 Å β = 108.6 ° |
| Formula units | Z = 4 |
| Twinning | frequently |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | measured: 3.17 to 3.46; calculated: [3.53] |
| Cleavage | well along {110} |
| Break ; Tenacity | uneven |
| colour | brown, greenish brown, light purple brown, black |
| Line color | gray-white |
| transparency | translucent |
| shine | Glass gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.683 to 1.722 n β = 1.684 to 1.722 n γ = 1.704 to 1.752 |
| Birefringence | δ = 0.021 to 0.030 |
| Optical character | biaxial positive |
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 [Si 2 O 6 ] and develops prismatic, up to one centimeter large, translucent crystals of gray-brown, greenish or black color.
Etymology and history
Pigeonite was first discovered at Pigeon Point in the US state of Montana and described in 1900 by Alexander Newton Winchell , who named the mineral after its type locality .
classification
In the structural classification of the International Mineralogical Association (IMA), pigeonite belongs together with enstatite , protoenstatite , clinoenstatite , ferrosilite and clinoferrosilite to the magnesium-iron proxenes (Mg-Fe-pyroxenes) in the pyroxene group .
In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the pigeonite belonged to the mineral class of "silicates and germanates" and there to the department of " chain and band silicates (inosilicates) ", where it belonged together with aegirin , augite , diopside , Esseneit , Hedenbergit , Jadeit , Jervisit , Johannsenite , kanoite , clino-enstatite , Klinoferrosilit , Kosmochlor , Namansilit , Natalyit , omphacite , Petedunnit and spodumene the subgroup of "clinopyroxene" with the system number. VIII / F.01 within the pyroxene group .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also assigns pigeonite to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)" a. However, this section is further subdivided according to the type of chain formation and membership of larger mineral families, so that the mineral can be classified accordingly in the sub-section “Chain and band silicates with 2-periodic single chains Si 2 O 6 ; Pyroxene family "can be found, where together with clinoenstatite, clinoferrosilite, halagurite and kanoite the" Mg, Fe, Mn-clinopyroxene, clinoenstatite group "with the system no. 9.DA.10 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns pigeonite to the class of "silicates and Germanates" and there in the section of "chain silicate minerals". Here it is together with Klinoenstatit, Klinoferrosilit and Kanoit in the group of "P2 / c Klinopyroxene" with the system no. 65.01.01 to be found within the subsection of " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".
Education and Locations
Pigeonite forms in highly heated mafic rocks such as basalt that are rapidly cooled. At the same time, only small amounts of calcium may be present for the formation , otherwise the similar mineral augite is formed. Typically this is the case in some volcanoes . In addition to these, it is also found in meteorites that have fallen to earth.
A typical example of a volcano that erupts pigeonite is the Soufrière Hills on the Caribbean island of Montserrat and an example of a meteorite find is the Cassigny meteorite in France.
In total, pigeonite has so far (as of 2011) been detected at around 120 sites. In addition to its type locality Pigeon Point, the mineral occurred in the United States in several places in the states of Alabama , Arizona , Maine , Massachusetts , Michigan , Nevada , New Mexico , Pennsylvania and Virginia as well as in the San Juan Mountains in Colorado, near Red Oak in Fulton County, Georgia , Lafayette, Indiana , Gray County (Kansas) , Beaver Bay , Minnesota, Stillwater County, Montana, Moore County, North Carolina , Shrewsbury , Rutland County, Vermont, Washougal in Washington and on the Potato River in Ashland County, Wisconsin .
In Germany one finds pigeonite among others Röhrnbach in the Bavarian Forest, at Bad Harzburg in Lower Saxony resin and Rockeskyll volcanic complex in the Rhineland-Palatinate Eifel .
Other localities are Algeria , the Antarctic , Australia , Brazil , China , Greenland , India , Cogne in Italy, Japan , the Yemen , Libya , Morocco , Whangarei in New Zealand, Oman , Papua New Guinea , Romania , Russia , Sweden , the Slovak Republic , Spain , St. Lucia , South Africa , South Korea , Stonařov in the Czech Republic, Hungary , Uzbekistan and the United Kingdom (Great Britain).
Pigeonite was also detected in rock samples from the moon , more precisely near the landing site of the Luna 16 mission in Mare Fecunditatis and in the lunar meteorite NWA 773 from Dchira (Western Sahara).
Crystal structure
Pigeonite crystallizes in the monoclinic crystal system in the space group P 2 1 / c (space group no. 14) and has the lattice parameters a = 9.71 Å , b = 8.95 Å, c = 5.25 Å and β = 108.6 ° with four formula units per unit cell .
Above 950 ° C the structure changes through a phase transition into a likewise monoclinic structure with the space group C 2 / c (space group no. 15) .
See also
Individual evidence
- ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X .
- ↑ Webmineral - Pigeonite (English)
- ↑ a b c Pigeonite at mindat.org (English)
- ^ A. Pabst: AN Winchell's observations on plagioclase, 1900; an historical note. In: Tschermaks Mineralogische und Petrographische Mitteilungen . tape 10 , 1965, p. 69-72 , doi : 10.1007 / BF01128616 . .
- ↑ Subcommite on Pyroxenes, CNMMN; Nobuo Morimoto: Nomenclature of Pyroxenes . In: The Canadian Mineralogist . tape 27 , 1989, pp. 143–156 ( mineralogicalassociation.ca [PDF; 1.6 MB ; accessed on March 30, 2019]).
- ↑ JM Schwartz, IS McCullum: Comparative study of equilibrated and unequilibrated eucrites: Subsolidus thermal histories of Haraiya and Pasamonte . In: American Mineralogist . tape 90 , 2005, pp. 1871-1886 .
- ↑ Mindat - localities for Pigeonite
- ↑ F. Cámara, MA Carpenter, MC Domeneghetti and V. Tazzoli: Non-convergent ordering and displacive phase transition in pigeonite: in situ HT XRD study. In: Physics and Chemistry of Minerals . tape 29 , 2002, pp. 331-340 , doi : 10.1007 / s00269-002-0241-y .
literature
- Pigeonit in: Anthony et al .: Handbook of Mineralogy , 1990, 1, 101 ( PDF )
