Phenacite
| Phenacite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Be 2 [4] [SiO 4 ] |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.AA.05 ( 8th edition : VIII / A.01) 51.01.01.01 |
| Crystallographic Data | |
| Crystal system | trigonal |
| Crystal class ; symbol | 3- |
| Space group | R 3 (No. 148) |
| Lattice parameters | a = 12.44 Å ; c = 8.23 Å |
| Formula units | Z = 18 |
| Physical Properties | |
| Mohs hardness | 7.5 to 8 |
| Density (g / cm 3 ) | measured: 2.93 to 3; calculated: 2.960 |
| Cleavage | good after {10 1 1}; clearly after {11 2 0} |
| Break ; Tenacity | shell-like |
| colour | colorless, white, yellow, rose-red, brown |
| Line color | White |
| transparency | transparent to translucent |
| shine | strong glass luster, fat luster |
| Crystal optics | |
| Refractive indices |
n ω = 1.650 to 1.656 n ε = 1.667 to 1.670 |
| Birefringence | δ = 0.017 |
| Optical character | uniaxial positive |
Phenakit is a rarely occurring mineral from the mineral class of "silicates and Germanates" with the chemical composition Be 2 [4] [SiO 4 ] and is therefore chemically seen a beryllium - silicate . Structurally, phenakite is one of the island silicates .
Phenakite crystallizes in the trigonal crystal system and develops mostly tabular to long prismatic crystals , but also occurs in the form of radial or granular mineral aggregates . Pure phenakite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline formation, it can also appear white and, due to foreign admixtures, take on a yellow, pink-red or brown color, the transparency decreasing accordingly.
Etymology and history
The mineral was named because of its similarity and therefore the likelihood of confusion with quartz after the ancient Greek word φέναξ [pʰénax] for "deceiver", which may with φαίνω [pʰai̯nɔː] "(appear), announce" (probably from * φάνjω * [pʰáni̯ɔː] ; cf. ai. vibhāva; related to φημί [pʰɛːmí] “to say” - from myk. <pa-si>, possible transcription : / pʰaːsí / “he says”, cf. Latin fārī “to speak”, old bajo “to tell ", Anord . Bōn and ags. Boen" prayer ") is related.
Phenakite was first found in 1833 in the emerald mine near Malysheva in Russia and described by Nils Gustaf Nordenskjöld (1792–1866), a Finnish mineralogist and traveler.
classification
In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) , the phenakite belongs to the division of " island silicates (nesosilicates)". However, the new Strunz'sche mineral classification now subdivides this department more precisely according to the presence or absence of further anions and the coordination of the cations in the crystal structure. The mineral can be found in the sub-section of "Island silicates without further anions and cations in tetrahedral [4] coordination", where it forms a separate group together with eucryptite , willemite and xingsaoite, which has not yet been confirmed by the IMA as an independent mineral .
The Dana system of minerals used in the English-speaking world also sorts the phenakite into the division of “ island silicates and SiO 4 groups only with cations in [4] coordination ”, where it forms the phenakite group as a lead mineral together with willemite and eucryptite .
Crystal structure
Phenacite crystallizes trigonal in the space group R 3 (space group no. 148) with the lattice parameters a = 12.44 Å and c = 8.23 Å as well as 18 formula units per unit cell .
Education and Locations
Phenakite forms either in igneous rocks such as granitic pegmatites or metamorphic rocks such as mica schist , but also through hydrothermal processes in greisen . It occurs there in paragenesis with apatite , beryl , chrysoberyl , fluorite , muscovite , quartz and topaz, among others .
Phenakite has been detected at over 260 sites worldwide (as of 2018). Above all, Brazil , Germany , France , Italy , Canada , Norway , Austria , Sweden , Switzerland and the United States are rich in phenakite finds (with three or more regions) .
Kragerø in Telemark (Norway) with crystal finds up to 25 cm in length and São Miguel de Piracicaba in Minas Gerais (Brazil), where crystals up to 10 cm long emerged, became known through finds of particularly large or well-developed crystals . Phenakites with a cat's eye effect have also been found in Sri Lanka .
Use as a gem stone
Phenakite is used exclusively as a gemstone . Despite its good physical (high hardness) and optical properties - its clear, lively glass luster can be sanded and polished to a greasy gloss - it is rarely found in stores. There is a risk of confusion with the colorless variety of quartz, rock crystal , but also with beryl , beryllonite , cerussite , danburite and topaz . Depending on the composition depending on the location, colored stones can, however, fade over time under the influence of light.
See also
literature
- Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 661 (first edition: 1891).
- Walter Schumann: Precious stones and gemstones. All kinds and varieties. 1900 unique pieces . 16th revised edition. BLV Verlag, Munich 2014, ISBN 978-3-8354-1171-5 , pp. 196 .
Web links
- Mineral Atlas: Phenakite (Wiki)
- American Mineralogist Crystal Structure Database - Phenakite (English)
Individual evidence
- ↑ a b c d e 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. 535 (English).
- ^ David Barthelmy: Phenakite Mineral Data. In: webmineral.com. Accessed December 31, 2018 .
- ↑ a b c Phenakite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 62 kB ; accessed on December 31, 2018]).
- ↑ a b c Phenakite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 31, 2018 .
- ↑ Nils Nordenskjöld: Beskrifning på Phenakit, ett nytt från mineral Urals . In: Kungl. Svenska vetenskapsakademiens handlingar . 1834, p. 160–165 ( limited preview in Google Book search).
- ↑ Find location list for phenakite in the Mineralienatlas and Mindat
- ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (= Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 193 .
- ↑ realgems.org - Phenakite with pictures of different cuts