Åkermanite
| Åkermanite | |
|---|---|
 Exhibited in the Mineralogical Museum of the University of Bonn |
|
| General and classification | |
| chemical formula | Ca 2 Mg [4] [Si 2 O 7 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.BB.10 ( 8th edition : VIII / C.02) 04.55.01.01 |
| Crystallographic Data | |
| Crystal system | tetragonal |
| Crystal class ; symbol | tetragonal-scalenohedral; 4 2 m |
| Space group | P 4 2 1 m (No. 113) |
| Lattice parameters | a = 7.84 Å ; c = 5.01 Å |
| Formula units | Z = 2 |
| Twinning | Crossing twins according to {100} and {001} |
| Physical Properties | |
| Mohs hardness | 5 to 6 |
| Density (g / cm 3 ) | measured: 2.944; calculated: 2.922 |
| Cleavage | clear after {001}, indistinct after {110} |
| Break ; Tenacity | uneven to scalloped |
| colour | colorless, yellowish gray, green, brown; colorless to yellow in thin layers |
| Line color | Please complete |
| transparency | transparent to translucent |
| shine | Glass gloss to resin gloss |
| Crystal optics | |
| Refractive indices |
n ω = 1.632 n ε = 1.640 |
| Birefringence | δ = 0.008 |
| Optical character | uniaxial positive |
| Other properties | |
| Special features | tends to decompose |
Åkermanite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the tetragonal crystal system with the chemical composition Ca 2 Mg [4] [Si 2 O 7 ] and is therefore chemically a calcium - magnesium silicate. Structurally, Åkermanit belongs to the group of silicates .
Åkermanite mostly develops short prismatic to thin tabular crystals , but also granular to massive mineral aggregates as well as cross twins . In its pure form it 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 yellowish-gray, green or brown color, the transparency decreasing accordingly.
With gehlenite (Ca 2 Al [4] [AlSiO 7 ]), Åkermanite forms a continuous mixed crystal row, with a coupled substitution of Al 3+ Al 3+ by Mg 2+ Si 4+ between the two end links . In addition, parts of the calcium can be replaced by sodium and potassium , magnesium by divalent iron and aluminum by trivalent iron.
Etymology and history
Åkermanite was first described in 1884 by IHL Vogt , who named the mineral after the Swedish metallurgist and metallurgical specialist Anders Richard Åkerman (1837–1922). For analysis purposes, he had made some melt products available in which the mineral or its synthetic equivalent was first discovered. Later, Åkermanite was also found as a natural mineral formation at various sites.
classification
In the meanwhile outdated, but still in use 8th edition of the mineral classification according to Strunz , the Åkermanite belonged to the mineral class of "silicates and germanates" and there to the department of " group silicates (sorosilicates)", where together with Andrémeyerite , barylite , gehlenite , gugiaite , Hardystonit , Jeffreyit , Kaliobarylith , melilite , Meliphan and Okayamalith the "melilite group" with the system number. VIII / C.02 formed.
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 Åkermanite to the class of "silicates and germanates" and there in the department of "group silicates (sorosilicates)". However, this section is further subdivided according to the type of silicate group formation, the possible presence of further anions and the coordination of the cations , so that the mineral according to its composition and structure in the subdivision “Si 2 O 7 groups, without non-tetrahedral anions; Cations in tetrahedral [4] and greater coordination ”can be found, where together with barylite, cebollite , gehlenite, gugiaite, hardystonite, jeffreyite, melilite and okayamalite the“ melilite group ”with the system no. 9.BB.10 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Åkermanite to the class of "silicates and germanates", but there in the more finely divided division of "group silicates: Si 2 O 7 groups, generally without additional anions" . Here he is together with Gehlenit, Melilith and Okayamalith in the "Melilith group" with the system no. 55.04.01 to be found within the subsection of the " Group silicates: Si 2 O 7 groups, generally without additional anions and with cations in [8] and lower coordination ".
Crystal structure
Åkermanite crystallizes tetragonally in the space group P 4 2 1 m (space group no. 113) with the lattice parameters a = 7.84 Å and c = 5.01 Å as well as 2 formula units per unit cell .
The crystal structure contains [Si 2 O 7 ] groups, which are arranged stretched with their longitudinal axis parallel to the c-axis. The cations calcium and magnesium are incorporated between the silicate groups, calcium being surrounded by eight oxygen ions each and magnesium by four oxygen ions each (see coordination number ).
properties
Åkermanite has a strong tendency to decompose .
Education and Locations
Åkermanite is mainly found as a crystalline component in iron and steel slag, but cement clinker can also contain Åkermanite and Melilite. In nature it forms through contact metamorphosis in silicic acid-containing limestone and dolomites as well as in sanidinite facies . Furthermore, Åkermanite can also arise in alkaline and calcium-rich igneous rocks . The accompanying minerals include diopside and its iron and aluminum-containing varieties Fassait , Forsterite , Grossular , Larnite , Merwinite , Monticellite , Spurrite and wollastonite .
A total of around 50 natural and anthropogenic (slag heaps) sites for Åkermanite are known worldwide so far (as of 2018) . In Germany, the mineral was found on the slag dump of the Herzog-Julius-Hütte near Astfeld in Lower Saxony and in the "Caspar" quarry on Ettringer Bellerberg near Ettringen in the Eifel in Rhineland-Palatinate.
Other sites include the Dupezeh mountain near Qala Diza ( Qeladze , قلعة دزة) in Iraq ; in the Hatrurim formation in the Israeli Negev desert ; on Monte Somma and Monte Cavalluccio near Sacrofano in Italy; at Hamada in Japan; Labrador , Oka and Saint-Joseph-du-Lac in Canada; on a slag dump near Tsumeb in Namibia; at Flekkeren in the Norwegian municipality of Skien ; in the basalt quarry near Also-Rákos ( Unter-Krebsenbach ) in the Harghita district in Romania; in the Odikhincha massif in the Krasnoyarsk region as well as in the Chibinen and near Kowdor on the Kola peninsula in Russia; near Kilchoan on the Scottish Ardnamurchan Peninsula ; at Söråker in Sweden; on the “Hendriksplaats Farm” near Mashishing (formerly Lydenburg ) and in the “Wessels Mine” near Hotazel in South Africa ; near Poličany / Kutná Hora (slag locality) and Želénky / Duchcov in the Czech Republic as well as on Iron Hill in Gunnison County (Colorado), on the Cascade Range (New York) and in the "Marble Canyon Mine" in Culberson County (Texas) in the United States from America.
See also
literature
- IHL Vogt: Studier over slagger I. In: Kong. Svenska Vetenskaps-Akademiens Handlingar . tape 9 , 1884, p. 3–302 ( rruff.info [PDF; 21.0 MB ; accessed on May 26, 2018]).
- IHL Vogt: The minerals of the Melilith group - namely gehlenite, melilite and a new tetragonal, non-Al 2 O 3 -containing (Ca, Mg) O-silicate (Åkermanite), together with intermediate links . In: Archives for Mathematics and Naturvidenskab . tape 13 , 1890, p. 310–402 ( rruff.info [PDF; 4,9 MB ; accessed on May 26, 2018]).
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 688 (first edition: 1891).
Web links
- Mineral Atlas: Åkermanite (Wiki)
- RRUFF Database-of-Raman-spectroscopy - Åkermanite (English)
- American-Mineralogist-Crystal-Structure-Database - Åkermanite (English)
Individual evidence
- ↑ a b c d e f Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 568 .
- ↑ Webmineral - Åkermanite (English)
- ↑ a b c d Åkermanite . 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; 65 kB ; accessed on May 26, 2018]).
- ↑ a b Mindat - Åkermanite (English)
- ↑ Martin Okrusch, Siegfried Matthes: Mineralogie. An introduction to special mineralogy, petrology and geology . 7th, completely revised and updated edition. Springer, Berlin [a. a.] 2005, ISBN 3-540-23812-3 , pp. 87 .
- ↑ a b c Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 709-712 .
- ↑ Mindat - Number of localities for Åkermanit
- ↑ Find location list for Åkermanit in the Mineralienatlas and Mindat