Astrophyllite
| Astrophyllite | |
|---|---|
 |
|
| General and classification | |
| chemical formula |
|
|
Mineral class (and possibly department) |
Silicates and germanates - chain and band silicates (inosilicates) |
|
System no. to Strunz and to Dana |
9.DC.05 ( 8th edition : VIII / G.12) 69.01.01.01 |
| Crystallographic Data | |
| Crystal system | triclinic |
| Crystal class ; symbol | triclinic pinacoidal; 1 |
| Space group | A 1 (No. 2, position 2) |
| Lattice parameters |
a = 5.36 Å ; b = 11.76 Å; c = 21.08 Å, α = 85.1 °; β = 90.0 °; γ = 103.2 ° |
| Formula units | Z = 2 |
| Frequent crystal faces | {100} |
| Physical Properties | |
| Mohs hardness | 3 |
| Density (g / cm 3 ) | measured: 3.2 to 3.4 |
| Cleavage | completely after {001}, indistinct after {100} |
| Break ; Tenacity | brittle |
| colour | bronze yellow to golden yellow, brown to reddish brown |
| Line color | white to brownish yellow; golden |
| transparency | opaque, translucent in thin layers |
| shine | Glass sheen, faint metallic sheen, pearlescent, greasy sheen |
| Crystal optics | |
| Refractive indices |
n α = 1.680 n β = 1.700 n γ = 1.730 |
| Birefringence | δ = 0.050 |
| Optical character | biaxial positive |
| Axis angle | 2V = 70 to 90 ° (measured); 80 ° (calculated) |
| Pleochroism | strong: X = dark red orange Y = orange yellow Z = lemon yellow |
Astrophyllite is a rather seldom occurring mineral from the mineral class of " silicates and germanates " with the idealized chemical composition K 2 NaFe 2+ 7 Ti 2 Si 8 O 26 (OH) 4 F.
Contained in the formula iron is, however, often by small amounts of in natural Astrophyllit manganese replaced . In addition, astrophyllite is structurally one of the chain and ribbon silicates with the additional anions oxygen , fluorine and hydroxides , which corresponds to the crystal-chemical structural formula developed by Strunz in the form K 2 Na (Fe 2+ , Mn 2+ ) 7 Ti 2 [ O 2 | F | (OH) 4 | Si 8 O 24 ] can be expressed.
Astrophyllite crystallizes in the triclinic crystal system and develops leafy to needle-like crystals , which are mainly arranged in the form of radial, star-shaped mineral aggregates . Occasionally it is also found ingrown with quartz . The mineral is generally opaque and only translucent in thin layers. The color of the glass to metallic shining crystals usually varies between bronze yellow and golden yellow, but can also be brown to reddish brown.
Etymology and history
Astrophyllite was first discovered on the island of Låven in the Langesundsfjord in the Norwegian province of Vestfold . The mineral was described in 1854 by Theodor Scheerer (1813–1875), who named it due to its leafy crystal formation and cleavage as well as its conspicuous star-shaped aggregate forms after the Greek words ἄστρον ástron for "star" and φύλλον phyllon for "leaf".
The type material of the mineral is kept in the mineralogical collection of the TU Bergakademie Freiberg (register no. 26246).
classification
In the outdated, but still in use 8th edition of the mineral classification according to Strunz , the astrophyllite belonged to the department of “transition structures between chain and layered silicates”, where it named the “astrophyllite series” with the system no. VIII / G.12 and the other members formed hydroastrophyllite , Kupletskit , Kupletskit- (Cs) , Lobanovit , Nalivkinit , Niobokupletskit , Niobophyllite and Zirkophyllite .
In contrast , the 9th edition of Strunz's mineral systematics , which has been in force since 2001 and is used by the International Mineralogical Association (IMA), classifies astrophyllite in the category of "chain and band silicates (inosilicates)". This is further subdivided according to the type of chain formation, so that the mineral can be found in the sub-section "Chain and ribbon silicates with branched 2-periodic single chains, Si 2 O 6 + 2SiO 3 → Si 4 O 12 " according to its structure , where the "astrophyllite group" with the system no. 9.DC.05 and the other members hydroastrophyllite, nalivkinite, kupletskit, kupletskit- (Cs), lobanovite, niobokupletskite, niobophyllite and zirconophyllite.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the astrophyllite to the class of "silicates and Germanates", although there it is in the more finely divided division of "chain silicates: chains with side branches or loops". Here, too, he is the namesake of the " astrophyllite group " with the system no. 69.01.01 within the subsection "Chain silicates: chains with side branches or loops with (P = 2, and N = 4, 2 side branches)".
Crystal structure
Astrophyllite crystallizes triclinically in space group A 1 (space group no. 2, position 2) with the lattice parameters a = 5.36 Å ; b = 11.76 Å; c = 21.08 Å; α = 85.1 °; β = 90.0 ° and γ = 103.2 ° as well as 2 formula units per unit cell .
properties
The mineral is strongly pleochroistic , i.e. depending on the direction from which the light penetrates the crystal, it is absorbed to different degrees and, in the case of astrophyllite, leads to a color change to dark red orange along the x-axis, orange-yellow along the y-axis and lemon yellow along the z-axis.
Education and Locations
Astrophyllit forms in basic intrusive rocks such as nepheline - syenites and alkaline granites and their pegmatites . In addition to nepheline, the accompanying minerals include albite , aegirine , arfvedsonite , biotite , jerfisherite , delayelite , eudialyte , catapleiite , cuplet kit , leucophane , natrolite , nepheline, rasvumite and zirconium .
As a rather rare mineral formation, astrophyllite can sometimes be abundant at various sites, but overall it is not very common. So far (as of 2017) around 190 sites are known to be known. Besides its type locality Låven the mineral yet occurred at several places in Langesundsfjorden such as on Årø ( Aroya ) Kjeøya , Stokkøya and the peninsula Vesterøya in Sandefjord and in Barkevik and Tvedalen province Vestfold and in some places in the provinces of Buskerud and Telemark on .
The largest known astrophyllite crystals and radial aggregates up to 10 centimeters in diameter were found at Eweslogtschorr in the Chibinen on the Russian Kola peninsula. Astrophyllites of similar size are known from the "St Peters Dome" about eight miles (≈ 13 km) southwest of Colorado Springs in El Paso County (Colorado) .
Other locations include Brazil, Chile, China, Greenland, Guinea, Canada, Kazakhstan, Kyrgyzstan, Malawi, Morocco, Mongolia, Namibia, Nigeria, Pakistan, Portugal, the East Siberian and northern regions of Russia, Slovakia, Spain, South Africa, Tajikistan, Ukraine and several states of the USA.
See also
literature
- T. Scheerer: Negotiations of the Bergmännischer Verein zu Freiberg . In: Berg- und Hüttenmännische Zeitung . tape 13 , 1854, pp. 239–240 ( rruff.info [PDF; 670 kB ; accessed on November 18, 2017]).
- Helmut Schrätze , Karl-Ludwig Weiner : Mineralogy. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 800 .
- 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. 473 .
Web links
- Mineral Atlas: Astrophyllite (Wiki)
- Webmineral - Astrophyllite (English)
- RRUFF Database-of-Raman-spectroscopy - Astrophyllite (English)
- American-Mineralogist-Crystal-Structure-Database - Astrophyllite (English)
Individual evidence
- ↑ a b c 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 .
- ↑ a b IMA / CNMNC List of Mineral List 2012 - Astrophyllite (PDF 1.6 MB)
- ↑ a b The numbering of this axis position does not correspond to the order of the International Tables for Crystallography , because it is not listed there.
- ^ A b c 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. 624 .
- ↑ a b c d e f Astrophyllite . 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; 79 kB ; accessed on November 18, 2017]).
- ^ Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp. 800 .
- ↑ a b c d e f g Mindat - Astrophyllite (English)
- ↑ Type material catalog of the University of Hamburg
- ↑ Mindat - Number of sites for astrophyllite (English)
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (= Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 248 .
- ↑ Type locality St Peters Dome, Cheyenne District (St. Peters Dome District), El Paso Co., Colorado, USA and astrophyllite images from this type locality (English)
- ↑ Find location list for astrophyllite in the Mineralienatlas and Mindat