Fairfieldite
| Fairfieldite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Ca 2 Mn 2+ (PO 4 ) 2 · 2H 2 O |
|
Mineral class (and possibly department) |
Phosphates, arsenates and vanadates |
|
System no. to Strunz and to Dana |
8.CG.05 ( 8th edition : VII / C.17) 02/40/02/01 |
| Crystallographic Data | |
| Crystal system | triclinic |
| Crystal class ; symbol | triclinic pinacoidal; 1 |
| Space group | P 1 (No. 2) |
| Lattice parameters |
a = 5.79 Å ; b = 6.57 Å; c = 5.51 Å, α = 102.2 °; β = 108.7 °; γ = 90.3 ° |
| Formula units | Z = 1 |
| Frequent crystal faces | {001}, {010}, {100}, {1 1 0}, { 1 1 1} |
| Physical Properties | |
| Mohs hardness | 3.5 |
| Density (g / cm 3 ) | measured: 3.08 to 3.11; calculated: 3.095 |
| Cleavage | perfect after {001}, good after {010}, clearly after {1 1 0} |
| Break ; Tenacity | uneven; brittle |
| colour | colorless, white, greenish-white, light yellow |
| Line color | White |
| transparency | transparent |
| shine | Pearl luster, faint diamond luster |
| Crystal optics | |
| Refractive indices |
n α = 1.633 to 1.640 n β = 1.641 to 1.650 n γ = 1.652 to 1.660 |
| Birefringence | δ = 0.019 to 0.020 |
| Optical character | biaxial positive |
| Axis angle | 2V = 86 ° (measured); 86 to 88 ° (calculated) |
Fairfieldite is a rarely occurring mineral from the mineral class of "phosphates, arsenates and vanadates". It crystallizes in the triclinic crystal system with the idealized chemical composition Ca 2 Mn 2+ (PO 4 ) 2 · 2H 2 O and is therefore chemically a water-containing calcium - manganese - phosphate . However, since naturally occurring fairfieldite usually has a small amount of manganese replaced ( substituted ) by iron , the formula is also given as Ca 2 (Mn, Fe) [PO 4 ] 2 · 2H 2 O in various sources .
Fairfieldite develops isometric to short prismatic crystals up to about three centimeters in size with a faint diamond luster on the surfaces, but can also be found in the form of leafy or lamellar as well as fibrous or radial mineral aggregates . In its pure form, Fairfieldite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline design , it can also appear white and, due to foreign admixtures, take on a greenish white or light yellow color, the transparency decreasing accordingly.
Etymology and history
Fairfieldite was first discovered in the "Fillow" quarry ( Branchville ) near Branchville in Fairfield County of the US state Connecticut and described in 1879 by George Jarvis Brush and Edward Salisbury Dana . They named the mineral after the county in which its type locality is located.
Type material of the mineral is stored at Yale University in New Haven (Connecticut) in the USA (catalog nos. 3.3118, 3.3123).
classification
Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the Fairfieldite belonged to the mineral class of "phosphates, arsenates and vanadates" and there to the department of "water-containing phosphates without foreign anions", where together with Roselith he created the "Fairfieldite -Roselith-Gruppe “with the system no. VII / C.17 and the other members brandtite , cassidyite , roselith-β ( roselith-beta ), collinsite , gaitite , hillite , messelite , parabrandtite , roselith, talmessite , wendwilsonite and zinc roselite .
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 Fairfieldite to the category of “phosphates etc. without additional anions; with H 2 O “. However, this is further subdivided according to the relative size of the cations involved and the molar ratio of the phosphate, arsenate or vanadate complex to the water of crystallization content , so that the mineral is classified in the sub-section “With large and medium-sized cations; RO 4 : H 2 O = 1: 1 "can be found where the" Fairfieldite group "with the system no. 8.CG.05 and the other members roselith-β, cassidyite, collinsite, gaitite, hillite, messelite, nickel valley messite , parabrandtite and talmessite.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Fairfieldite to the class of "phosphates, arsenates and vanadates" and there in the department of "water-containing phosphates etc.". Here it is together with in the " Fairfieldite subgroup (Triklin: P 1 ) " with the system no. 40.02.02 to be found in the subsection "Water-containing phosphates etc., with A 2+ (B 2+ ) 2 (XO 4 ) × x (H 2 O)".
Crystal structure
Fairfieldite crystallizes triclinic in the space group P 1 (space group no. 2) with the lattice parameters a = 5.79 Å ; b = 6.57 Å; c = 5.51 Å; α = 102.2 °; β = 108.7 ° and γ = 90.3 ° and one formula unit per unit cell .
Education and Locations
Fairfieldite forms as an accessory component in granitic pegmatites . As accompanying minerals may include apatite , Diadochite , Dickinsonit , Eosphorit , Jahnsit , Mitridatit , muscovite , quartz , rhodochrosite , Rockbridgeite , Stewartit , Strunzit and a variety of other Fe-Mn phosphates occur.
As a rare mineral formation, Fairfieldite could only be detected at a few localities, whereby so far (as of 2014) around 70 localities are known. In addition to its type locality quarry "Fillow" in Fairfield County (Connecticut), the mineral occurred in the United States in the Midnight Owl Mine and in the White Picacho District in Yavapai County in Arizona, on Chief Mountain in San Diego County in California, in Clay Canyon at Fairfield in Utah County , Utah, and in several locations in various counties in Maine , New Hampshire , North Carolina, and South Dakota .
In Germany, Fairfieldite was discovered at the Hennenkobel ( Hühnerkobel ) in the Bavarian Forest and near Hagendorf ( Waidhaus ) in the Upper Palatinate Forest in Bavaria.
In Austria, the mineral has so far only been found in a spodumene test mining on the ridge of fire , about 2 km southwest of the Weinebene on the Koralpe in Carinthia (see also Mining in Carinthia ) and the only known site in Switzerland so far is the Pontetal near Brissago TI im Canton of Ticino.
Other sites are in Argentina, Australia, Brazil, Finland, Iran, Italy, Canada, Morocco, Namibia, Poland, Portugal, Russia, Sweden and the Czech Republic.
See also
literature
- George J. Brush, Edward S. Dana: On the mineral locality in Fairfield County, Connecticut, with the description of two additional new species. Second paper . In: American Journal of Science and Arts . tape 17 , 1879, p. 359–368 ( rruff.info [PDF; 478 kB ; accessed on February 11, 2018]).
- Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 641 .
- Fanfani, A. Nunzi, PF Zanazzi: The crystal structure of fairfieldite . In: Acta Crystallographica . B26, 1970, p. 640-645 .
- Sasha Herwig, Frank C. Hawthorne: The topology of hydrogen bonding in brandtite, collinsite and fairfieldit . In: The Canadian Mineralogist . tape 44 , 2006, pp. 1181–1196 ( rruff.info [PDF; 3.3 MB ; accessed on February 11, 2018]).
Web links
- Mineral Atlas: Fairfieldite (Wiki)
- Webmineral - Fairfieldite
- Database-of-Raman-spectroscopy - Fairfieldite
- American-Mineralogist-Crystal-Structure-Database - Fairfieldite
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names - Fairfieldite
- ↑ a b c d Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 483 .
- ↑ a b c d e Fairfieldite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 64 kB ; accessed on February 11, 2018]).
- ↑ a b c d e Mindat - Fairfieldite
- ↑ Malcom E. Back: Fleischer's Glossary of Mineral Species . 11th edition. Mineralogical Record, Tucson, Arizona (AZ) 2014, p. 79 .
- ^ Mindat - Number of localities for Fairfieldite
- ↑ Find location list for Fairfieldite in the Mineralienatlas and Mindat