Stokesite

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Stokesite
Stokesite-Albite-221148.jpg
Stokesite on albite of the Cleavelandite variety from the pegmatite "Córrego do Urucum" near Galiléia, Doce Valley, Minas Gerais, Brazil (step size: 3.1 cm × 2.5 cm × 2.4 cm)
General and classification
chemical formula CaSn [Si 3 O 9 ] • 2H 2 O
Mineral class
(and possibly department) 		Silicates and Germanates - chain silicates and band silicates (inosilicates)
System no. to Strunz
and to Dana 		9.DM.05 ( 8th edition : VIII / F.29)
65.05.01.01
Similar minerals plaster
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-dipyramidal; 2 / m  2 / m  2 / m
Space group Pnna (No. 52)Template: room group / 52
Lattice parameters a  = 14.465  Å ; b  = 11.625 Å; c  = 5.235 Å
Formula units Z  = 4
Frequent crystal faces {100}, {211}
Physical Properties
Mohs hardness ≈ 6
Density (g / cm 3 ) 3.185 (measured); 3.211 (calculated)
Cleavage very perfect according to (101), imperfect according to (100)
Break ; Tenacity clamshell; brittle
colour colorless to white, pinkish-light brown to pale brown; colorless in reflected light
Line color White
transparency transparent
shine Glass luster, on {100} pearlescent luster
Crystal optics
Refractive indices n α  = 1.609 to 1.618; 1.609
n β  = 1.612 to 1.619; 1.6125
n γ  = 1.619 to 1.628; 1.619
Refractive index n  = 1.616
Birefringence δ = 0.010
Optical character biaxial positive
Axis angle 2V = 69.5 ° (measured); 2V = 66 ° to 70 ° (calculated)
Other properties
Chemical behavior insoluble in concentrated HCl

Stokesite is a rare mineral from the mineral class of silicates and germanates . It crystallizes in the orthorhombic crystal system with the composition CaSn [Si 3 O 9 ] · 2H 2 O, so it is a water-containing calcium - tin - chain silicate .

Stokesite is found in the form of prismatic crystals with a maximum size of 1 cm or spherical and radial-fiber aggregates up to 3 cm in size.

The type locality of the Stokesits is also called Roscommon Cliff "Stamps and Jowl Zawn" ( coordinates of Roscommon Cliffs ) at Botallack in the mining area St Just not far from St Just in Penwith in the county of Cornwall in England .

Etymology and history

George Gabriel Stokes - the Stokesite was named in his honor

In the summer of 1899, the British mineralogist Arthur Hutchinson (1866-1937) was busy sorting the collection of minerals acquired by Joseph Carne (1782-1858) for the Cambridge Mineralogical Museum. A 10 mm long crystal from the St Just mining area, sitting on axinite and labeled as plaster, aroused his interest. The strange paragenesis led him to a complete chemical and crystallographic investigation, as a result of which the crystal turned out to be a new mineral. After an initial preliminary note, Arthur Hutchinson published the description of the new mineral in the British science magazine "Mineralogical Magazine".

He named it after his colleague at the University of Cambridge , the British- Irish mathematician and physicist George Gabriel Stokes (1819–1903). Among other things, Stokes was the discoverer of the law named after him and dealt with fluorescence , which he was the first to name and whose nature he was the first to recognize.

The type material for stokesite is in the Mineralogical Museum of the University of Cambridge.

For more than 62 years, attempts were made to find further evidence of this mineral at the type locality, but the type level remained the only level of this mineral type. It was not until 1961 that another stokesite site became known - the lithium pegmatite "Ctidružice", Znojmo (Znaim), South Moravian region , followed by another find in 1966 in the "Pegmatite Věžná I" near Věžná , Okres Pelhřimov , Žďár nad Sázavou district , highlands , both in the Czech Republic , followed. After a maximum 7 mm large Stokesite aggregate on albite and orthoclase , partially speared by acicular tourmaline crystals , was found in June 1975 in the “Halvosso Quarry” near Mabe , formerly “Wendron & Falmouth District”, also in Cornwall The 76 year long search at the type locality finally succeeded. The well-known mineral collector and dealer Richard Barstow ( namesake for the barstowite ), who also succeeded in finding the stokesite from the "Halvosso Quarry", was able to find a 4 mm large stokesite crystal on axinite in the "Wheal Cock Zawn" on Roscommon Cliff to recover.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the stokesite belonged to the mineral class of "silicates and germanates" and there to the department of "chain silicates and band silicates (inosilicates)", where it together with calciohilairite , gaidonnayite , georgechaoite , Hilairit , Komkovit , Pyatenkoit- (Y) and Sazykinait- (Y) the stokesite group with the system no. VIII / F.29 .

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 the Stokesite to the class of "Silicates and Germanates" and there in the department of "Chain and band silicates (Inosilicates)" a. This department is, however, further subdivided according to the type of chain formation, so that the mineral can be found in the subdivision “Chain and band silicates with 6-periodic single chains, Si 6 O 18 ”, where the unnamed group is the sole representative 9.DM.05 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Stokesite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here he is the sole representative in the unnamed group with the system no. 65.05.01 to be found in the sub-section " Chain Silicates : Simple unbranched chains, W = 1 with chains P = 6 ".

Chemism

Seven microprobe analyzes on Stokesite from the "Halvosso Quarry" quarry resulted in mean values ​​of 34.78% SnO 2 ; 0.33% FeO; 0.37% MnO; 12.85% CaO; 43.08% SiO 2 and 8.59% H 2 O (calculated from the difference). Analysis in the absence of FeO and MnO showed 35.79% SnO 2 ; 12.86% CaO; 42.89% SiO 2 and 8.46% H 2 O. On the basis of eleven oxygen atoms , the empirical formula Ca 0.97 Sn 1.00 Si 3.01 O 9 · 2.03H 2 O was calculated CaSn [Si 3 O 9 ] · 2H 2 O has been simplified.

Stokesite is the only mineral with the element combination Ca - Sn - Si - O - H. Eakerite , Ca 2 SnAl 2 Si 6 O 18 (OH) 2 · 2H 2 O are chemically similar ; Kristiansenit , Ca 2 SCSN (Si 2 O 7 ) (Si 2 O 6 OH); and silesiaite , Ca 2 Fe 3+ Sn (Si 2 O 7 ) (Si 2 O 6 OH).

Crystal structure

Crystal structure of stokesite as a "polyhedron model". Color legend: silicon tetrahedron: dark blue; Tin octahedron: purple; Calcium polyhedron: green-blue; Oxygen: red.
Crystal structure of the Stokesite with unbranched six-single chains

Stokesite crystallizes in the orthorhombic crystal system in the space group Pnna (space group no. 52) with the lattice parameters a = 14.465  Å ; b = 11.625 Å and c = 5.235 Å as well as four formula units per unit cell . The first X-ray diffractometric analyzes were carried out by Gay & Rickson as early as 1960. Template: room group / 52

The crystal structure of the Stokesits (compare with the adjacent pictures of the structure) consists of periodic six single chains of SiO 4 - tetrahedra which are linked through shared oxygen atoms. The tetrahedra chains are in the direction of [010] by the sharing of oxygen atoms with SnO 6 - octahedron and CaO 4 (H 2 O) 2 - polyhedron connected. Sn is coordinated by six oxygen atoms belonging to the chains, Ca is coordinated by four oxygen atoms belonging to the chains and by two oxygen atoms belonging to the water molecules.

properties

morphology

At its type locality, stokesite forms a maximum of 1 cm large, prismatic crystals on which the anterior pinacoid {100} and the orthorhombic dipyramid {211} determine the costume . The pinacoid {010} as well as {655} and {221} were identified as further surface shapes at the type locality. Areas of the form (101) can arise due to the very perfect cleavage. Crystals from the "Halvosso Quarry" show the very clear flat shapes {100}, {110}, {011}, {101}, {301} and {111} as well as {010}, {130}, {5.13.0}, {5.12.0}, {490}, {120}, {211}, {221}, {243}, {485}, {353}, and {823}, the latter shapes being rough or curved or both. The supporting forms of these crystals are {485}, {243} and {211}. The maximum 1 mm large Stokesite crystals from Huanggang / China represent combinations of the dominant pinacoids {100} and {010} as well as the rhombic dipyramid {344}. Small stokesite crystals mainly show the rhombic dipyramids, whereas larger crystals are plate-shaped . In La Cabrera, Spain, tabular crystals up to 1 cm in size, stretched along the a-axis [100], with the surface shapes that determine the costume {001}, {104} and {111} as well as the subordinate shapes {011} were found and {210}. The basic pinacoid {001} is the dominant form; it shows a six-sided outline, since the surfaces of the dipyramid {111} are dominant compared to those of the prism {011}. The shapes {001} and {104} often have a deep stripe parallel [010]. In addition to clear crystals, stokesite is also found in spherical and radial-fiber aggregates up to 3 cm in size, the spherical aggregates being particularly typical of the pegmatite "Córrego do Urucum" in Brazil.

  • Costume and habitus of Stokesite crystals (the same colors mean the same surface shapes)

  • “Halvosso Quarry” near Mabe in Cornwall, extremely extensive

  • Roscommon Cliff at Botallack (type locality), St Just, Cornwall

  • Huanggang Deposit, Chifeng, Inner Mongolia, China

  • La Saludadora, La Cabrera, Valdemanco, Madrid, Spain

physical and chemical properties

Stokesite is colorless to white or pinkish-light brown to pale brown, but its line color is always white. The surfaces of the transparent Stokesite show a glass-like, {100} pearlescent sheen , which goes well with the values ​​for light refraction (n α  = 1.609 to 1.618; n β  = 1.612 to 1.619; n γ  = 1.619 to 1.628) and for birefringence (δ = 0.010) matches. Under the microscope the mineral is colorless in transmitted light and therefore does not show any pleochroism .

Stokesite has a very perfect cleavage according to (101) and an imperfect cleavage according to (100). Due to its brittleness , however , it breaks in a similar way to quartz , with the fracture surfaces being shell-shaped. With a Mohs hardness of ≈ 6, stokesite is one of the medium-hard minerals and, like the reference mineral orthoclase (hardness 6), can still be scratched with a steel file. The calculated density for the mineral is 3.185 g / cm³, the calculated density was found to be 3.211 g / cm³.

There is no information on fluorescence in UV light or on cathodoluminescence under the electron beam for the mineral.

Stokesite is infusible in front of the soldering tube and is insoluble in concentrated hydrochloric acid , HCl. It shows no flame coloring and gives a silica skeleton in the phosphorus salt bead.

Education and Locations

Stokesite with oxystannomicrolite on albite from the pegmatite "Córrego do Urucum" (field of view: approx. 1 cm)
Stokesite on Schörl from the pegmatite "Córrego do Urucum" (step size: 12.0 cm × 5.7 cm × 4.3 cm)

Tin-bearing pegmatites or calcareous skarns provide the elements calcium, tin and silicon necessary for the formation of stokesite. The mineral slowly crystallizes in low-temperature hydrothermal conditions in open spaces, e.g. B. the surfaces or the spaces between previously formed minerals. Crystallization of the stokesite is tied to late-stage tin-rich hydrothermal fluids that can occur in different geological environments. Various educational conditions can therefore be assumed for stokesite.

  • In pegmatitic deposits such as Ctidružice, "Věžná I" and "Córrego do Urucum", the stokesite formed during the alteration of cassiterite . In Ctidružice, the stokesite was formed during the albitization of the pegmatite and was deposited like a sandwich in tiny cracks of the fine-grain cassiterite. In Věžná, stokesite was deposited on albite in Druze within a desilicated pegmatite. In the Sn-rich skarns of Kozlov, stokesite is formed during the alteration of tin silicates, particularly of tin-containing andradite . In La Cabrera, the stokesite was found in a miarolithic cavity in a granite pegmatite on albite and microcline as well as smoky quartz , whereby stokesite is a low-temperature hydrothermal formation. The succession is indicated with muscovite → albite / microcline → stokesite.
  • Most of the other deposits and occurrences of the stokesite are of the "calcareous skarn type". In the Cornwall deposits, stokesite was formed during contact metamorphosis or metasomatosis. In Huanggang / China the elements Si, Ca, Sn and Fe released from the skarns during the dissolution of primary rock-forming minerals accumulated in the hydrothermal solutions, migrated through cracks and fissures and later became in the form of low-temperature mineral associations on magnetite megacrysts in the Druze deposited.

Typical accompanying minerals of the stokesite are axinite (Fe) and cassiterite (Roscommon Cliff); Albite of the variety "Cleavelandite", titanite , beryl and "microlite" ( oxystannomicrolite ) ("Córrego do Urucum"); Chlorite or clinochlor , adulara , cassiterite, tin-containing clinozoisite and tin-containing titanite (Bögl quarry near Dörfel); Muscovite, albite, microcline and quartz (La Cabrera, Spain); as well as magnetite, calcite , andradite, Vesuvian , cassiterite, fluorite , quartz , “mica” and clinochlor (Huanggang).

As a very rare mineral formation, the Stokesite could so far (as of 2018) only be described from around 20 sites. The type locality for Stokesite is also called Roscommon Cliff "Stamps and Jowl Zawn" at Botallack in the mining area St Just not far from St Just in Penwith in the county of Cornwall in England . Stokesite was also found on the neighboring "Wheal Cock Zawn" west of the Roscommon Cliffs and in the "Halvosso Quarry" near Mabe , the former "Wendron & Falmouth District", also in Cornwall.

The only point of discovery in Germany is the “Bögl quarry” near Dörfel not far from Schlettau , Annaberg-Buchholz district, Ore Mountains , Saxony .

Further findings are:

Locations for Stokesite from Austria and Switzerland are therefore unknown.

use

Due to its rarity, stokesite is of no practical importance, but due to its training it is very popular with mineral collectors.

See also

literature

  • Arthur Hutchinson: On Stokesite, a new mineral containing tin, from Cornwall . In: Mineralogical Magazine . tape 12 , no. 57 , 1900, pp. 274–281 , doi : 10.1180 / minmag.1900.012.57.07 (English, rruff.info [PDF; 354 kB ; accessed on September 16, 2018]).
  • AG Couper, AM Clark: Stokesite crystals from two localities in Cornwall . In: Mineralogical Magazine . tape 41 , 1977, pp. 411–414 (English, minersoc.org [PDF; 404 kB ; accessed on September 16, 2018]).
  • Stokesite . 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; 77 kB ; accessed on September 18, 2018]).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 735 (first edition: 1891).
  • 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. 504 .

Web links

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

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y Arthur Hutchinson: On Stokesite, a new mineral containing tin, from Cornwall . In: Mineralogical Magazine . tape 12 , no. 57 , 1900, pp. 274–281 , doi : 10.1180 / minmag.1900.012.57.07 (English, rruff.info [PDF; 354 kB ; accessed on September 16, 2018]).
  2. ↑ a b c d e f P. Gay, KO Rickson: X-ray data on stokesite . In: Mineralogical Magazine . tape 32 , 1960, pp. 433–435 (English, rruff.info [PDF; 108 kB ; accessed on September 16, 2018]).
  3. ↑ a b c d Atso Vorma: Crystal structure of stoke site, CaSnSi 3 O 9 · 2H 2 O . In: Mineralogical Magazine . tape 33 , 1963, pp. 615–617 (English, rruff.info [PDF; 116 kB ; accessed on September 16, 2018]).
  4. ↑ a b c d e f g h i j k l m Stokesite . 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; 77  kB ; accessed on September 18, 2018]).
  5. ↑ a b c d e Jacques P. Cassedanne: The Urucum Pegmatite, Minas Gerais, Brazil . In: The Mineralogical Record . tape 17 , no. 5 , 1986, pp. 307-314 (English).
  6. ↑ a b c d e f g Mindat - Stokesit , accessed on September 18, 2018 (English)
  7. ↑ Arthur Hutchinson: On stoke site - a new mineral from Cornwall . In: The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science . tape 48 , no. 294 , 1899, pp. 480–481 , doi : 10.1080 / 14786449908621439 (English, tandfonline.com [PDF; 286 kB ; accessed on September 16, 2018]).
  8. ^ A b František Čech: Occurrence of stokesite in Czechoslovakia . In: Mineralogical Magazine . tape 32 , no. 252 , 1961, pp. 673–675 , doi : 10.1180 / minmag.1961.032.252.01 (English, minersoc.org [PDF; 140 kB ; accessed on September 16, 2018]).
  9. ^ A b Petr Černý: A new Czechoslovak occurrence of stokesite . In: Mineralogical Magazine . tape 35 , 1966, pp. 835–837 (English, minersoc.org [PDF; 144 kB ; accessed on September 16, 2018]).
  10. ^ AG Couper, Richard W. Barstow: Rediscovery of Stokesite Crystals in Cornwall, England . In: The Mineralogical Record . tape 8 , no. 4 , 1977, pp. 294-297 (English).
  11. ^ A b c d AG Couper, AM Clark: Stokesite crystals from two localities in Cornwall . In: Mineralogical Magazine . tape 41 , 1977, pp. 411–414 (English, minersoc.org [PDF; 404 kB ; accessed on September 16, 2018]).
  12. ↑ Steffen Jahn: The world's best Stokesite and some other mineralogical news from Brazil . In: Mineral World . tape 12 , no. 4 , 2001, p. 8-9 .
  13. ↑ a b c Atso Vorma: The crystal structure of stoke site, CaSnSi 3 O 9 · 2H 2 O . In: Bulletin de la Commission Géologique de Finlande . No. 228 , 1963, pp. 1–48 (English, gtk.fi [PDF; 10.5 MB ; accessed on September 16, 2018]).
  14. ^ Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  649 .
  15. ↑ a b c d e f g Xue Yuan, Li Guowu, Yang Guangming: Mineralogy and Crystallography of Stokesite from Inner Mongolia, China . In: The Canadian Mineralogist . tape 55 , no. 1 , 2017, p. 63–74 , doi : 10.3749 / canmin.1600045 (English).
  16. ↑ a b c José González del Tánago, Rafael Pablo Lozano, Alfredo Larios, Ángel La Iglesia: Stokesite crystals from La Cabrera, Madrid, Spain . In: The Mineralogical Record . tape 43 , no. 4 , 2012, p. 499-508 (English).
  17. ^ A b John Sampson White: What's new in minerals . In: The Mineralogical Record . tape 4 , no. 6 , 1973, p. 275-276 (English).
  18. ↑ a b Stefan Weiß, Olaf Martin: Alpinotype fissures and fluorite dikes: The quarry Dörfel near Annaberg, Saxony . In: Lapis . tape 38 , no. 2 , 2013, p. 14–28 and 54 .
  19. ↑ Mindat - Number of localities for Stokesite , accessed on September 18, 2018 (English)
  20. ↑ Find location list for samsonite at the Mineralienatlas and at Mindat (accessed on September 18, 2018)
  21. ↑ Michael Trinkler: Dignified Indium, Stokesite and Heinrichit - three new finds from the western Ore Mountains . In: Geologica Saxonica: Journal of Central European Geology . tape 56 , no. 1 , 2010, p. 3–8 ( senckenberg.de [PDF; 333 kB ; accessed on September 16, 2018]).
  22. ↑ Lee A. Groat, R. James Evans, Jan Cempírek, Catherine McCammon, Stanislav Houzar: Fe-rich and As-bearing vesuvianite and wiluite from Kozlov, Czech Republic . In: The American Mineralogist . tape 98 , no. 7 , 2013, p. 1330–1337 , doi : 10.2138 / am.2013.4358 (English).
  23. ↑ Nikao et al .: Stoke site in the region of Ena, Gifu prefecture . In: Chigaku Kenkyu (Geoscience Magazine) . tape 28 , 1977, pp. 149-152 (Japanese).
  24. ↑ Ritsuro Miyawaki, Izumi Nakai, Kozo Nagashima, Akiyoshi Okamoto, Toshi Isobe: The first occurences of hingganite, hellandite and wodginite in Japan . In: Journal of the Mineralogical Society of Japan . tape 18 , no. 1 , 1987, pp. 1–48 , doi : 10.2465 / gkk1952.18.17 (Japanese, jst.go.jp [PDF; 2.9 MB ; accessed on September 16, 2018] with an English abstract).
  25. ↑ Philippe M. Sonnet: Burtite, calcium Hexahydrostannate, a new mineral from El Hamman, Central Morocco . In: The Canadian Mineralogist . tape 19 , no. 3 , 1981, p. 397-401 (English).
  26. ↑ Anatoly Vasil'evich Voloshin, Yakov A. Pakhomovskiy: On the stokesite from granitic pegmatite on Kola Peninsula and in sharn from Karelia (Piotkyaranta) . In: New data on Minerals . tape 9 , no. 35 , 1988, pp. 36-39 (Russian).
  27. ↑ Jörgen Langhof, Erik Jonson, Lars Gustafsson, Bertil Otter: Utö - en Klassisk svensk mineralfyndort (Kongsberg Mineral Symposium 1998) . In: Bergverksmuseets Skrift . tape 14 , 1998, pp. 29–31 (Swedish, nags.net [PDF; 2.7 MB ; accessed on September 16, 2018] with an English abstract).
  28. ^ Eugene E. Foord: Famous Mineral Localities: the Himalaya Dike System, Mesa Grande District, San Diego County, California . In: The Mineralogical Record . tape 8 , no. 6 , 1977, pp. 461-474 (English).