Rhodicite

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Rhodicite
Rhodicite-27526.jpg
Yellow rhodicite from the Sahatany pegmatite field, Manandona Valley, Vakinankaratra , Madagascar (size 4.4 cm × 3.2 cm × 1.5 cm)
General and classification
chemical formula
  • KBe 4 Al 4 (B 11 Be) O 28
  • (K, Cs) Al 4 Be 4 [O 4 | B 11 BeO 24 ]
Mineral class
(and possibly department) 		Borates (formerly carbonates, nitrates and borates )
System no. to Strunz
and to Dana 		6.GC.05 ( 8th edition : V / L.02)
5.08.02.01
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic-hexakistrahedral; 4  3  m
Space group P 4 3 m (No. 215)Template: room group / 215
Lattice parameters a  = 7.32  Å
Formula units Z  = 1
Frequent crystal faces {001} and { 1 11}
Twinning rarely after {111}
Physical Properties
Mohs hardness 8 to 8.5
Density (g / cm 3 ) measured: 3.22 to 3.44; calculated: 3.2 to 3.62
Cleavage indistinct after {111} and { 1 11}
Break ; Tenacity shell-like
colour colorless to white, light gray, light yellow to sulfur yellow, rarely green
Line color White
transparency transparent to translucent
shine Glass gloss to weak diamond gloss
Other properties
Special features strong piezoelectric and pyroelectric

Rhodizite is a rarely occurring mineral from the mineral class of " borates " (formerly carbonates, nitrates and borates , see classification ). It crystallizes in the cubic crystal system with the idealized chemical composition KBe 4 Al 4 (B 11 Be) O 28 , so it is a potassium - beryllium - aluminum borate. However, since some of the potassium in naturally occurring rhodicites can be represented ( substituted ) by cesium (up to about 4%) and / or rubidium , the formula is also used in various sources with (K, Cs) Al 4 Be 4 [O 4 | B 11 BeO 24 ] or (K, Cs, Rb) Al 4 Be 4 [O 4 | B 11 BeO 24 ].

Rhodizit usually develops dodecahedral and tetrahedral crystals up to about 3.5 centimeters in size with a glass-like to slightly diamond-like sheen on the surfaces. In its pure form, Rhodizite is colorless and transparent. However, due to multiple refraction due to lattice construction defects or polycrystalline training, it can also appear white and, due to foreign admixtures, take on a light gray, light yellow to sulfur yellow and rarely green color, the transparency decreasing accordingly.

With a Mohs hardness of 8 to 8.5, Rhodizite is one of the minerals with "precious stone hardness", which corresponds to that of the reference mineral topaz (8) or that of chrysoberyl (8.5).

Due to its chemical relationship with londonite as a cesium analogue of rhodicite and its similarity to boracite in terms of crystal shape and color, rhodicite can easily be confused with these minerals.

Etymology and history

Rhodizit was first discovered by Gustav Rose , who found small, white crystals of a previously unknown mineral on some red, Siberian tourmalines that were kept in the Royal Mineralogical Museum of Berlin (now the Museum für Naturkunde (Berlin) ). The area around the village of Shaitanka about 60 werst (corresponds to approx. 64 km) north of Yekaterinburg ( Katharinenburg ) in the Sverdlovsk Oblast is given as the exact location . Shaitanka and the nearby village of Sarapulka are considered a type locality .

Rose analyzed and described the mineral in 1834 and named it after its characteristic property of coloring the soldering tube flame bright red, after the ancient Greek word ῥοδίζω [rhodízō] for red coloring .

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the rhodicite belonged to the common mineral class of "carbonates, nitrates and borates" and there to the division of "framework borates with [BO 2 ] 1− to [B 6 O 10 ] 2− ”, where together with Hambergite he created the“ Hambergite-Rhodizite Group ”with the system no. V / L.02 and the other member Londonit .

The 9th edition of Strunz's mineral systematics, valid since 2001 and used by the International Mineralogical Association (IMA), assigns the rhodicite to the now independent class of “borates” and there in the department of “heptaborates and other megaborates”. This is further subdivided according to the crystal structure , so that the mineral can be found in the sub-section "Tekto-Dodecaborate" according to its structure, where it only forms the unnamed group 6.GC.05 together with Londonite .

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking area , assigns the rhodicite like the outdated Strunz systematics to the common class of “carbonates, nitrates and borates” and there to the department of “anhydrous borates with hydroxyl or halogen”. Here it can also be found together with Londonit in the unnamed group 08/25/02 within the sub-section “ Anhydrous borates with hydroxyl or halogen ”.

Crystal structure

Rhodicite crystallizes cubically in the space group P 4 3 m (space group no. 215) with the lattice parameter a  = 7.32  Å and one formula unit per unit cell . Template: room group / 215

properties

Rhodizit has strong piezoelectric and pyroelectric properties, reacts to changing, elastic deformation or heating and cooling with electrical polarization .

In front of the soldering tube , rhodicite is difficult to melt, whereby primarily the edges melt like glass-like white and opaque and form irregular outgrowths. The melted area glows bright yellowish red during the process. The flame itself first turns green and then also bright red. Even when annealed on coal, the mineral only melts round the edges and becomes opaque white.

Education and Locations

Beige-colored, octahedral rhodicite from the Sahatany pegmatite field, Manandona Valley, Vakinankaratra, Madagascar (size: 4.3 cm × 4.1 cm × 3.7 cm)

Rhodicite forms magmatic as an accessory component in alkali-rich granite - pegmatites . In addition to tourmaline (primarily elbaite or rubellite ), albite , behierite , beryl , londonite, microcline , quartz and spodumene can also occur as accompanying minerals .

As a rare mineral formation, Rhodizite could only be detected at a few localities, whereby so far (as of 2013) around 20 localities are known. The villages Shaitanka and Sarapulka, which are considered type localities, are the only known sites in Russia so far .

Known by exceptional Rhodizitfunde including the Antandrokomby- and Sahatany Valley are in the region Vakinankaratra on Madagascar , where up to three centimeters, cubic and tetrahedral crystals were found. Other previously known sites in Madagascar are Andrembesoa in the Betafo district ( Vàkinankàratra region ) in the Antananarivo province and the Ambatofinandrahana and Ambositra ( Amoron'i Mania region ) in the Fianarantsoa province.

The only other known location so far is Fern in Florence County (Wisconsin) in the USA.

use

Despite its high hardness, Rhodizite is of no interest for commercial use as a gemstone , as it only forms small and very seldom high-quality, transparent crystals. Occasionally he is but for collectors ground offered in faceted shape.

See also

literature

  • Gustav Rose : About the Rhodizite, a new type of mineral . In: Annals of Physics and Chemistry . tape 33 , 1834, pp. 253–256 ( rruff.info [PDF; 241 kB ; accessed on September 30, 2017]).
  • A. Pring, VK Din, DA Jefferson, JM Thomas: The crystal chemistry of rhodizite: a re-examination . In: Mineralogical Magazine . tape 50 , March 1986, p. 163–172 ( rruff.info [PDF; 768 kB ; accessed on September 30, 2017]).

Web links

Commons : Rhodizite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; October 2013 (PDF 1.5 MB)
  2. ↑ 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.  360 .
  3. ↑ a b c d e Rhodicite . 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 September 30, 2017]).
  4. ↑ Webmineral - Rhodicites
  5. ↑ 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 .
  6. ↑ a b Gustav Rose : Ueber den Rhodizit, a new mineral genus . In: Annals of Physics and Chemistry . tape  33 , 1834, pp. 253–256 ( rruff.info [PDF; 241 kB ; accessed on September 30, 2017]).
  7. ↑ Mindat - Number of locations for Rhodizit
  8. ↑ Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Nebel Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 134 .
  9. ↑ Find location list for Rhodizit in the Mineralienatlas and Mindat
  10. ^ 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. 236 .