Zinc staurolite
| Zinc staurolite | |
|---|---|
| General and classification | |
| other names |
IMA 1992-036 |
| chemical formula |
|
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.AF.30 ( 8th edition : VIII / B.03) 02.02.03.03 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / m (No. 12) |
| Lattice parameters |
a = 7.853 Å ; b = 16.534 Å; c = 5.639 Å β = 90.00 ° |
| Formula units | Z = 1 |
| Physical Properties | |
| Mohs hardness | 7 to 7.5 |
| Density (g / cm 3 ) | calculated: 3.78 |
| Cleavage | Please complete |
| colour | colorless, brownish yellow, reddish brown |
| Line color | White |
| transparency | transparent |
| shine | Glass gloss to resin gloss |
| Crystal optics | |
| Refractive indices |
n α = 1.722 n γ = 1.734 |
| Birefringence | δ = 0.012 |
| Optical character | biaxial positive |
Zinc staurolite , also zinc ostaurolite or Zincostaurolite (English: Zincostaurolite or zincian staurolite ), is a very rarely occurring mineral of the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition Zn 2 Al 9 Si 4 O 23 (OH) and develops mostly transparent, prismatic crystals up to about 3 mm in size, which are either colorless or brownish-yellow, reddish-brown in color.
As a zinc- dominated analogue, zinc staurolite forms a mixed series with the iron- dominated staurolite and the magnesium- dominated magnesia staurolite .
Etymology and history
Zinc staurolite was first found in 1992 on the Brunegghorn in the Swiss municipality of Zermatt in the uppermost Mattertal and recognized as an independent mineral under the no. IMA1992-036 . The mineral was first described by Christian Chopin, Bruno Goffe, Luciano Ungaretti and Roberta Oberti, who named the mineral based on its close relationship with staurolite and its zinc content and described and named it in 2003 in the European Journal of Mineralogy 15, 167-176 published.
classification
Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , zinc staurolite belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates with non-tetrahedral anions (Neso-subsilicates)", where it, together with gerstmannite , Klinoedrite , Magnesiostaurolite , Staurolite and Stringhamite the "staurolite group" with the system no. VIII / B.03 .
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies zinc staurolite in the category of "island silicates (nesosilicates)". This is further subdivided according to the possible presence of additional anions as well as the coordination of the cations involved , so that the mineral according to its composition and structure in the subsection "F. Island silicates with additional anions; Cations in [4] he, [5] he and / or only [6] he coordination ”can be found, where the“ staurolite group ”with system no. Is only found together with magnesiostaurolite and staurolite. 9.AF.30 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns zinc staurolite to the class of "silicates and germanates" and there in the section of "island silicates: SiO 4 groups and O, OH, F and H2O". Here it can be found together with staurolite and magnesiostaurolite in the unnamed group 52.02.03 within the subsection " Island silicates: SiO 4 groups and O, OH, F and H2O with cations in [4] and> [4] coordination".
Crystal structure
Zinc ostaurolite crystallizes monoclinically in the space group C 2 / m with the lattice parameters a = 7.853 Å ; b = 16.534 Å; c = 5.639 Å and β = 90.00 ° and one formula unit per unit cell .
Zinc ostaurolites from metabauxites of the Mesozoic Barrhorn series (Zermatt, Swiss Western Alps) were examined in more detail . In addition to zinc, they contain significant amounts of lithium (Li + ) and iron. The full structural formula is:
M4 (Fe 2+ 0.13 Mg 0.10 vac 3.77 ) T2 (Zn 2.45 Li 0.51 Fe 2+ 0.20 vac 0.84 ) M1.2 (Al 15.98 Ti 0.02 ) M3 (Al 1.95 Mg 0.09 vac 1.96 ) T1 (Si 8 ) O 44.33 (OH) 3.67
In this structural formula vacancies are as vac (English vacancy : space) reported.
These zinc ostaurolites contain an above-average amount of lithium. The reason for this is not an unusually high Li content of the total rock, but the presence of large tetrahedral gaps (T2) in the staurolite structure compared to other rock-forming minerals . This means that staurolites absorb the entire amount of cations in a rock for which such a large tetrahedral gap is particularly favorable in terms of energy (e.g. Li + and Zn 2+ ).
The M4 octahedral gap is only occupied by a few cations (0.23 apfu). Each M4 octahedron is connected to two T2 tetrahedra by common faces. The distance between an M4 and a T2 gap is so small that a common occupation of neighboring T2 and M4 positions can be excluded. With an even distribution of the cations on the M4 positions, two T2 positions should be empty for each occupied M4 position. In fact, there are significantly more (3.65 vacancies on T2 per occupied M4 position). This indicates that in Zn staurolites, in contrast to Fe and Mg staurolites, vacancies in the tetrahedral position T2 are not or only to a small extent coupled to the occupation of the M4 position.
Education and Locations
Zinc ostaurolite is formed during the metamorphosis of bauxites from around 400 ° C, probably from gahnite , pyrophyllite , diaspore . In addition to staurolite, it occurs in paragenesis with various other minerals such as allanite , anchorite , apatite , chloritoid , cookite , diaspore, gahnite, kaolinite , kyanite , margarite , muscovite , paragonite , pyrite , pyrophyllite, rutile , tourmaline and zircon .
World could Zinkostaurolith so far (as of 2010) are detected at five localities: On the east coast of the Greek island of Samos , in the " Bleikvassli Mine" in the Norwegian municipality Hemnes , in the Palladium - Gold - deposit at Maldynyrd and on Grubependity Lake in the Republic of Komi, which is part of the Russian Federation, and at its aforementioned type locality Brunegghorn in the Swiss Mattertal.
See also
literature
- Christian Chopin, Bruno Goffe, Luciano Ungaretti, Roberta Oberti: Magnesiostaurolite and zincostaurolite: mineral description with a petrogenetic and crystal-chemical update . In: European Journal of Mineralogy . tape 15 , 2003, p. 167-176 , doi : 10.1127 / 0935-1221 / 2003 / 0015-0167 .
- John L. Jambor, Andrew C. Roberts: New Mineral Names . In: American Mineralogist . tape 88 , 2003, p. 1626–1629 ( rruff.info [PDF; 299 kB ; accessed on April 29, 2018]).
Web links
- Mineral Atlas: Zinc Staurolite (Wiki)
- Mineral data sheet Zincostaurolite at the Mineralogical Association of Canada (English, PDF 46.7 kB)
Individual evidence
- ↑ a b IMA / CNMNC List of Mineral Names - Zincostraurolite (English, PDF 1.67 MB; p. 209)
- ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
- ↑ Webmineral - Zincostaurolite (English)
- ↑ a b c American Mineralogist Crystal Structure Database - Zincostaurolite (English)
- ↑ a b c Mindat - Zincostaurolite (English)
- ^ 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. 869 .