Crocite

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Crocite
Crocoite-360746.jpg
Crocoite from the Adelaide Mine, Dundas, Tasmania , Australia
(size: 4.0 × 4.0 × 2.5 cm)
General and classification
other names
chemical formula Pb [CrO 4 ]
Mineral class
(and possibly department) 		Sulfates (and relatives, see classification )
System no. to Strunz
and to Dana 		7.FA.20 ( 8th edition : VI / E.01)
03/35/01/01
Similar minerals Cinnabarit , realgar
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / n (No. 14, position 2)Template: room group / 14.2
Lattice parameters a  = 7.13  Å ; b  = 7.44 Å; c  = 6.80 Å
β  = 102.4 °
Formula units Z  = 4
Frequent crystal faces {110}, {120}, {111}; subordinate also {001}, { 3 01}, { 4 01}
Physical Properties
Mohs hardness 2.5 to 3
Density (g / cm 3 ) measured: 6.0 to 6.1; calculated: [6.10]
Cleavage clear after {110}, indistinct after {001} and {100}
Break ; Tenacity small mussels to uneven
colour yellow, yellowish orange, orange, hyacinth red
Line color orange yellow
transparency transparent to translucent
shine Diamond shine to greasy shine
Crystal optics
Refractive indices n α  = 2.290 (2)
n β  = 2.360 (2)
n γ  = 2.660 (2)
Birefringence δ = 0.370
Optical character biaxial positive
Axis angle 2V = 57 ° (measured); 54 ° (calculated)
Pleochroism weak: X = Y = red orange; Z = blood red

Crocoite , outdated also known as red lead ore or chromic acid lead and its chemical name lead chromate , is a rarely occurring mineral from the mineral class of " sulfates (including selenates , tellurates , chromates , molybdates and tungstates )" with the chemical composition Pb [CrO 4 ] .

Crocoite crystallizes in the monoclinic crystal system and sometimes develops very shaped, but mostly long, prismatic to needle-shaped crystals up to about 15 centimeters in length, which are stretched and striped parallel to the c-axis. The crystal ends are often unfinished and often hollow. Radial tufts of randomly grown crystals and occasionally also coarse masses and crusty coatings are just as common.

The color of the transparent to translucent crystals varies from strong yellow to yellow orange to bright hyacinth red with a fat to diamond-like sheen . However, under the influence of light, the color can fade over time.

With a Mohs hardness of 2.5 to 3, crocoite lies between the reference minerals gypsum (2) and calcite (3) and can therefore be scratched with a copper coin.

Etymology and history

Dried saffron threads

The mineral was first mentioned in 1763 in a travel report by Mikhail Wassiljewitsch Lomonossow , who after his return from Saint Petersburg reported that Johann Gottlob Lehmann , who worked there as a professor of chemistry, had a “red lead from Siberia” or “red lead ore from Berezovsk ”(today Beryozovsky (Sverdlovsk) ) discovered and investigated. This designation can be found shortened to "Roth Bleierz" ( red lead ore ) in the records of Abraham Gottlob Werner . In his somewhat more detailed description from 1766, Lehmann pointed out, among other things, that the mineral dissolved in hydrochloric acid resulted in a solution with a beautiful green color and also found lead in the compound, but not a new element. However, Lehmann was unable to complete his investigations because he died in an explosion in his laboratory in 1767.

The exact determination of the composition of the mineral caused unusual difficulties for many analysts and Martin Heinrich Klaproth also failed because he did not have enough material available. It was not until Louis-Nicolas Vauquelin who succeeded in analyzing the material in 1797 and was able to isolate the previously unknown element chromium from the compound.

In 1832, François Sulpice Beudant coined the name "Crocoïse" from the ancient Greek word κρόκος [krókos] for saffron , as the striking color of the mineral reminded him of the color of dried saffron threads. In its description, plomb chromaté , plomb rouge , Roth lead ore , chrome lead and chromic acid lead are also listed as synonyms . In his 4th edition of the Mineral Systematics published in 1854, James Dwight Dana described the name form coined by Beudant as a bad choice and referred to the modification of the name by Franz von Kobell to Crocoisit , published in 1838 , according to the form customary in mineralogical nomenclature. A final adaptation of the name to the form Krokoit, which is still valid today, was made in 1841 by August Breithaupt , which was also adopted by Dana in his 5th edition of the mineral systematics in 1868.

In contrast, the name Kallochrom , which was handed down by Friedrich Hausmann in 1813, from the Greek κάλλος for beauty and χρώμα for color, is no longer in use .

Henry James Brooke and William Hallowes Miller described a new mineral in 1852 and designated it after its discoverer, Johann Gottlob Lehmann as Lehmannit . However, in later investigations it turned out that this mineral was identical in composition to the already known crocoite. The mineral name lehmannite was therefore discredited and has been a synonym for crocoite ever since.

As precise type locality today (2014) the pit "Tsvetnoi" on the mountain Uspenskaya applies in gold - deposit Beryozovsky ( Berezovsk , Berezovsky ), Sverdlovsk Oblast in the Russian Ural Mountains . Type material of the mineral is kept in the Muséum national d'histoire naturelle in Paris .

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , the crocoite belonged to the class of "sulfates, chromates, molybdates, wolframates" (including some selenates and tellurates) and there to the department of "chromates", where it was named after the "tarapacáit- Krokoit-Gruppe "with the system no. VI / E.01 and the other members Chromatit and Tarapacáit ( Tarapacait ) formed.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VI / F.01-30 . In the “Lapis system” this also corresponds to the section “Chromates [CrO 4 ] 2- ”, where crocoite, together with chromatite and tarapacáite, forms an independent but unnamed group.

The 9th edition of Strunz's mineral systematics , which has been valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also classifies crocoite in the “chromates” department. However, this section is further subdivided according to the possible presence of further anions , so that the mineral can be found according to its composition in the sub-section “With additional anions” (without further specification), where it is the only member of the unnamed group 7.FA.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the crocoite to the class of "sulfates, chromates and molybdates" (including selenates, tellurates, selenites, tellurites and sulphites), but in the more finely divided division of "anhydrous chromates" " a. Here he is to be found as the only member of the unnamed group 35.03.01 within the subdivision of " Anhydrous chromates with A + XO 4 ".

Chemism

The idealized, theoretical composition of crocoite Pb [CrO 4 ] consists of 64.11% by weight of lead (Pb), 16.09% by weight of chromium (Cr) and 19.80% by weight of oxygen (O). Depending on the location occasionally small amounts of chromium can by sulfur (S) and lead by zinc (Zn) replaces be.

At high temperatures crocoite can form mixed crystals with anglesite (Pb [SO 4 ]).

Crystal structure

Crocoite crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a  = 7.13  Å ; b  = 7.44 Å; c  = 6.80 Å and β = 102.4 ° and 4 formula units per unit cell . Template: room group / 14.2

Structurally Krokoit similar to monazite , but with [CrO 4 ] 2+ - tetrahedra and Pb 2+ ions which of seven O 2- ions are from seven different tetrahedra surrounded as its nearest neighbor.

In addition to the monoclinic crocoite, there is also an orthorhombic modification that can be produced synthetically by chemical precipitation of lead chromate. Rhombic lead chromate has the lattice parameters a  = 8.67 ± 0.03 Å, b  = 5.59 ± 0.01 Å and c  = 7.13 ± 0.02 Å, but it is unstable and changes to stable after a short time monoclinic crocite around.

Crystal structure of crocoite

  • looking parallel to the a-axis

  • looking parallel to the b-axis

  • looking parallel to the c-axis

  • spatial representation in the standard crystallographic orientation

Color table: __ Pb     __ Cr     __ O

properties

morphology

Crocoite crystal with strongly striped prismatic surfaces

Crocoite forms richly shaped, prismatic crystals with the habit- defining surfaces {110}, {120} and {111}. {001}, { 3 01} and { 4 01} are also subordinate . The prism surfaces are striped parallel to the c-axis [001] and the prisms are often hollow.

Chemical and physical properties

In front of the soldering tube , crocoite melts easily ( melting point : 844 ° C) and crackles heavily. It evaporates on charcoal and forms a lead-containing slag, and when heated on phosphorus salt or borax pearls, they are colored emerald green as a reaction to the chromium it contains.

Crocoite dissolves in hot hydrochloric acid , releasing chlorine and separating out PbCl 2 . It also dissolves in potassium hydroxide (KOH) with a brown color.

Under UV light , some crocoites show a dark brown fluorescence .

Modifications and varieties

In 1858 , August Breithaupt designated a mineral acquired by General-Major von Jossa in Beresow as jossaite, which occurs in small yellow-orange to orange-colored crystals on vauquelinite and was regarded as zinc-containing lead chromate. Jossaite is now considered a mixture of crocoite and smithsonite .

Education and Locations

Dundasite (white) and crocoite from Dundas (Tasmania)
Crocoite and pyromorphite (green) from the type locality Berjosowski, Yekaterinburg, Urals, Russia (field of view: 1.5 cm)

Krokoit forms as rare secondary mineral in the oxidation zone of chromium-containing lead - and galena - deposits . Various lead and chromium minerals such as Anglesite , Cerussite , Descloizit , Dundasite , Embreyite , Phenicochroit , Pyromorphite , Vanadinite , Vauquelinite, Wulfenite as well as Quartz and Limonite occur as accompanying minerals .

As a rare mineral formation, crocoite could only be detected in a few places so far (status: 2014), whereby around 90 sites have been documented (status 2019). In addition to its type locality in the Tsvetnoi mine and other mines in the vicinity of the Berjosowski gold deposit ( Berezovsk ), where crystals of up to 4 cm in length were sometimes found, the mineral was also found in Russia in the Mednorudyanskoye copper deposit near Nižne Tagil ( Nizhnii Tagil ) and at the hamlet of Tochilnyi Kljutsch northwest of Resch in the Sverdlovsk Oblast and on Sukhovyaz near Verkhny Ufalei in the Chelyabinsk Oblast .

In Germany, crocoite was found on the Mechernich lead mountain and in the "Grünbleiberg" mine near Niedergelpe in North Rhine-Westphalia and near Callenberg in the Saxon district of Zwickau.

In Austria, the mineral is so far only known from the Alpleskopf and Dirstentritt near the North Tyrolean community of Nassereith .

The best and largest crystal specimens so far were found in the mining area around Dundas on Tasmania in Australia, where crystals up to 10 cm long could be recovered in several pits. Especially from the "Adelaide Mine" steps from several centimeters to over 25 cm in size emerged.

Other locations are among others in Brazil, Chile, China, France, Italy, Canada, the Democratic Republic of the Congo (Zaire), Mexico, Namibia, the Philippines, Romania, Zimbabwe, Slovakia, South Africa, Tajikistan, in the United Kingdom (UK) and the United States of America (USA).

use

Despite its high chromium content of up to 16.09%, crocoite is of no importance as an ore, even if the mineral was mined in Tasmania for some time. As a synthetically produced lead chromate , it is often used as so-called “chrome yellow” in varnishes and emulsion paints .

Even as a jewelery stone , crocoite is not to be used in trade, despite its beautiful color and gloss, as it is too soft and therefore too sensitive. In rare cases, however , it is cut in the shape of a gemstone, usually a step cut , for collectors .

See also

literature

  • JG Lehmann: News of a new real Bleyerze . In: Hamburg magazine or collected publications on teaching and enjoyment from nature research and the pleasant sciences in general . tape 11 , 1767, pp. 336–348 ( limited preview in Google Book search).
  • WF Petterd: A catalog of the minerals known to occur in Tasmania, with notes on their distribution . In: Papers and Proceedings of the Royal Society of Tasmania for 1893 . June 1894, p. 24–25 (English, available online at rruff.info [PDF; 3.2 MB ; accessed on April 25, 2019]).
  • H. Effenberger, F. Pertlik: Four monazite type structures: comparison of SrCrO4, SrSeO4, PbCrO4 (crocoite), and PbSeO4 . In: Journal of Crystallography . tape 176 , 1986, pp. 75–83 (English, available online at rruff.info [PDF; 735 kB ; accessed on April 25, 2019]).

Web links

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

Individual evidence

  1. ^ 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.  415 .
  2. ↑ a b c d e f g h Helmut Schrätze , Karl-Ludwig Weiner : Mineralogie. A textbook on a systematic basis . de Gruyter, Berlin; New York 1981, ISBN 3-11-006823-0 , pp.  598-599 .
  3. ↑ a b c d Crocoite . 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; 67  kB ; accessed on April 24, 2019]).
  4. ↑ a b c Crocoite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 24, 2019 .
  5. ↑ a b c A. G. Betechtin (А. Г. Бетехтин): Textbook of special mineralogy . 2nd Edition. VEB Verlag Technik, Berlin 1957, p.  397–398 (Russian: Курс минералогии . Translated by Wolfgang Oestreich).
  6. ↑ a b Per Enghag: Encyclopedia of the Elements. Technical Data - History - Processing… John Wiley & Sons, 2008, ISBN 978-3-527-61234-5 , pp. 576 ( limited preview in Google Book search).
  7. ↑ Johann Carl Freiesleben (Ed.): Abraham Gottlob Werner's last mineral system: Edited from his estate by order of the Mining Authority and provided with explanations . Freyberg / Vienna 1817, p.  22 ( limited preview in Google Book search).
  8. ↑ a b c Hans Lüschen: The names of the stones. The mineral kingdom in the mirror of language . 2nd Edition. Ott Verlag, Thun 1979, ISBN 3-7225-6265-1 , p. 303 .
  9. ^ E. Schweda: Jander / Blasius: Inorganic Chemistry I - Introduction & Qualitative Analysis . 17th edition. Hirzel, 2012, ISBN 978-3-7776-2134-0 , pp. 346 .
  10. ^ Henry George Liddell, Robert Scott: A Greek-English Lexicon - κρόκος. In: perseus.tufts.edu. Perseus Digital Library, accessed April 24, 2019 .
  11. ↑ FS Beudant: Crocoïse, plomb chromate . In: Traité Élémentaire de Minéralogie . 2nd Edition. tape 2 . Paris 1832, p. 669–670 (French, rruff.info [PDF; 83 kB ; accessed on April 24, 2019]).
  12. ↑ Franz von Kobell : Fundamentals of Mineralogy: Designed for use in lectures and for self-study . Schrag , Nuremberg 1838, p.  282 ( limited preview in Google Book search).
  13. ^ Si and Ann Frazier: CROCOITE: What's in a name? In: Pacific Northwest Chapter. Friends of Mineralogy. Newsletter March 2004 Bulletin . 2004, p. 9 (English, available online at pnwfm.org [PDF; 375 kB ; accessed on April 24, 2019]).
  14. ^ Lehmannite (of Brooke). In: mindat.org. Hudson Institute of Mineralogy, accessed April 24, 2019 .
  15. ↑ Details on the type locality Tsvetnoi on Uspenskaya Mountain in the Berezovskoye Au deposit, Sverdlovsk Oblast, Urals, Russia at the Mineral Atlas and Mindat
  16. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  17. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed April 19, 2019 .
  18. ^ A b David Barthelmy: Crocoite Mineral Data. In: webmineral.com. Retrieved April 24, 2019 .
  19. ↑ 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.  684 .
  20. ↑ G. Collotti, L. Conti, M. Zocchi: The structure of the orthorhombic modification of lead chromate PbCrO 4 . In: Acta Crystallografica . tape 12 , 1959, pp. 416 , doi : 10.1107 / S0365110X59001220 (English).
  21. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp.  617–618 (first edition: 1891).
  22. ^ A b 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. 56, 224 .
  23. ^ Albert Huntington Chester: A dictionary of the names of minerals including their history and etymology . 1st edition. John Wiley & Sons, London 1896, p. 139 (English, available online at archive.org  - Internet Archive - keyword Jossaite ).
  24. ↑ CF Rammelsberg: Handbuch der Mineralchemie . Verlag von Wilhelm Engelmann, Leipzig 1860, p. 300 ( available online at archive org  - Internet Archive ).
  25. ↑ Jossaite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 24, 2019 .
  26. ↑ Indra Günther: Old mineral names and synonyms. (PDF 2.65 MB) In: indra-g.at. September 17, 2009, accessed April 24, 2019 (Jossait, p. 82).
  27. ↑ Localities for Crocoite. In: mindat.org. Hudson Institute of Mineralogy, accessed April 24, 2019 .
  28. ↑ a b Petr Korbel, Milan Novák: Mineral Encyclopedia (=  Dörfler Natur ). Edition Dörfler im Nebel-Verlag, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 152 .
  29. ↑ Image of a crocoite step from the Adelaide Mine, Dundas, over 25 cm in size. In: mindat.org. Hudson Institute of Mineralogy, accessed April 24, 2019 .
  30. ↑ Find location list for crocoite in the Mineralienatlas and Mindat .
  31. ↑ Crocoite. In: realgems.org. Michael RW Peters, October 10, 2010, accessed April 25, 2019 .