Cafetit

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Cafetit
Cafetite, Lizardite-529436.jpg
Yellow-orange, tabular cafetite crystals in a matrix of lizardite (image width 0.7 mm)
General and classification
chemical formula
  • CaTi 2 O 5 · H 2 O
  • (Ca, Mg) (Fe 3+ , Al) 2 Ti 4 O 12 · 4H 2 O
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.FL.75 ( 8th edition : IV / D.20)
07/08/03/01
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  = 4.9436 (15)  Å ; b  = 12.109 (4) Å; c  = 15.911 (5) Å
β  = 98.937 (5) °
Formula units Z  = 8
Frequent crystal faces {100}, {520}, {210}
Physical Properties
Mohs hardness 4 to 5
Density (g / cm 3 ) measured: 3.28; calculated: 3.19
Cleavage Please complete!
Break ; Tenacity brittle; elastic in needle-like training
colour colorless, yellow
Line color White
transparency transparent to translucent
shine Diamond luster
Crystal optics
Refractive indices n α  = 1.950
n β  = 2.080
n γ  = 2.110
Birefringence δ = 0.160
Optical character biaxial negative
Axis angle 2V = 36.5 ° to 39 ° (measured); 48 ° (calculated)

Cafetite is a very rarely occurring mineral from the mineral class of "oxides and hydroxides" with the idealized chemical composition CaTi 2 O 5 · H 2 O and is therefore chemically a water-containing calcium - titanium - oxide .

Cafetit crystallizes in the monoclinic crystal system and develops mostly needle-like to columnar crystals with striped prismatic surfaces. In addition, it is also found in the form of fibrous, tangled mineral aggregates and masses. The transparent to translucent crystals are usually light yellow to colorless, but can also take on an orange-brown color.

Etymology and history

Cafetit was first discovered in the Afrikanda massif (Russian: Африканда) in the Murmansk Oblast on the Russian Kola Peninsula . The mineral was first described in 1959 by Alexander Alexandrowitsch Kucharenko , WW Kondratjewa and WM Kowjasina, who named it after its chemical composition of Ca, Fe and Ti.

Type material of the mineral is in the Mineralogical Museum of the University of Saint Petersburg under the catalog no. 13420-21 and in the Fersman Museum in Moscow under catalog no. 72024 kept.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the cafetite belonged to the mineral class of "oxides and hydroxides" and there to the department of "oxides with a molar ratio of metal: oxygen = 1: 2 (MO 2 and related compounds) “, Where together with Kassit , Kobeit- (Y) and Lucasit- (Ce) it formed the unnamed group IV / D.20 .

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 cafetite to the class of "oxides and hydroxides", but in the department of "hydroxides (without V or U) " a. This is further subdivided according to the possible presence of hydroxide ions and / or crystal water as well as the crystal structure , so that the mineral according to its composition and structure in the subsection “Hydroxides with H 2 O ± (OH); Layers of edge-linked octahedra “can be found, where it is the only member of the unnamed group 4.FL.75 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the cafetite to the class of "oxides and hydroxides", but there in the department of "multiple oxides with Nb, Ta and Ti". Here he is to be found as the only member of the unnamed group 08.07.03 within the sub-section “ Multiple oxides with Nb, Ta and Ti ”.

Crystal structure

Cafetit crystallizes monoclinically in the space group P 2 1 / n (space group no. 14, position 2) with the lattice parameters a  = 4.9436 (15)  Å ; b  = 12.109 (4) Å; c  = 15.911 (5) Å and β = 98.937 (5) ° and 8 formula units per unit cell . Template: room group / 14.2

Education and Locations

Light yellow cassite spherulites with yellow-orange, tabular cafetite crystals in a matrix of lizardite from the Val di Serra quarry, Pilcante, Ala , Province of Trentino, Italy (image width 2 mm)

Cafetite forms in miarolitic cavities during the late cooling phase of igneous rocks , predominantly in pegmatites and pyroxenites . The accompanying minerals include anatase , baddeleyite , ilmenite , cassite , clinochlor , perovskite , phlogopite , titanite and titanomagnetite .

In addition to its type locality in the Afrikanda massif, which is south-west of the Chibinen and south of Lake Imandra , the mineral was found in Russia at the Kukiswumtschorr in the Chibinen and in the Kowdor mine in the mountain massif of the same name in the Murmansk Oblast.

So far (as of 2017), cafetit has only been found worldwide in the Cava Val di Serra quarry (municipality of Ala ) in the Italian province of Trentino . Another site near Gordon Butte in Meagher County of the US state Montana is doubtful or has not yet been confirmed.

See also

literature

  • AA Kukharenko, VV Kondrat'Eva, VM Kovyazina: Cafetite, a new hydrous titanate of calcium and iron . In: Zapiski Vserossijskogo Mineralogicheskogo Obshchestva . tape 88 , no. 4 , 1959, pp. 444–453 (Russian, rruff.info [PDF; 830 kB ; accessed on November 22, 2017]).
  • Michael Fleischer : New mineral names . In: American Mineralogist . tape 45 , 1960, pp. 476-480 ( rruff.info [PDF; 294 kB ; accessed on November 22, 2017]).

Web links

Commons : Cafetite  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; September 2017 (PDF 1.67 MB)
  2. ^ 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.  247 .
  3. ↑ Webmineral - Cafetite (English)
  4. ↑ a b c d e Cafetite . 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; 70  kB ; accessed on November 21, 2017]).
  5. ↑ a b Sergey V. Krivovichev, Victor N. Yakovenchuk, Peter C. Burns, Yakov A. Pakhomovsky, Yury P. Menshikov: Cafetite, Ca [Ti 2 O 5 ] (H 2 O): Crystal structure and revision of chemical formula . In: American Mineralogist . tape 88 , 2003, p. 424–429 ( rruff.info [PDF; 2.0 MB ; accessed on November 22, 2017]).
  6. ↑ a b c d e Mindat - Cafetite (English)
  7. ↑ 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 .
  8. ↑ Mineral Atlas : Type locality Afrikanda - Африканда
  9. ↑ Find location list for Cafetit at the Mineralienatlas and at Mindat