Tilleyit

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Tilleyit
Tilleyite-171531.jpg
Tilleyite from the Crestmore Quarry, Crestmore, Riverside County, California, USA (size: 4.3 × 4.0 cm)
General and classification
chemical formula
  • Ca 5 Si 2 O 7 (CO 3 ) 2
  • Ca 5 [(CO 3 ) 2 | Si 2 O 7 ]
Mineral class
(and possibly department) 		Silicates and germanates - group silicates (sorosilicates)
System no. to Strunz
and to Dana 		9.BE.82 ( 8th edition : VIII / B.06)
56.02.09.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / a (No. 14, position 3)Template: room group / 14.3
Lattice parameters a  = 15.11  Å ; b  = 10.24 Å; c  = 7.58 Å
β  = 105.2 °
Formula units Z  = 4
Twinning lamellar after {100}
Physical Properties
Mohs hardness not defined
Density (g / cm 3 ) measured: 2.82 to 2.84; calculated: 2.88
Cleavage completely after {20 1 }, indistinct after {100} and {010}, very indistinct after {001}
colour colorless, white
Line color White
transparency transparent to translucent
shine frosted
Crystal optics
Refractive indices n α  = 1.612 to 1.617
n β  = 1.632 to 1.635
n γ  = 1.652 to 1.654
Birefringence δ = 0.040
Optical character biaxial positive
Axis angle 2V = 85 to 90 ° (measured); 88 to 90 ° (calculated)

Tilleyite is a rarely occurring mineral from the mineral class of " silicates and germanates " with the chemical composition Ca 5 [(CO 3 ) 2 | Si 2 O 7 ] and thus, chemically speaking, a calcium silicate with additional carbonate ions. Structurally, Tilleyite belongs to the group silicates .

Tilleyite crystallizes in the monoclinic crystal system and forms only poorly developed, irregularly defined, tabular crystals and rounded grains. In its pure form it is colorless and transparent. However, due to multiple light refraction due to lattice defects or polycrystalline design , it can also appear white, with the transparency correspondingly decreasing.

Etymology and history

Tilleyite was first discovered in a quarry near Crestmore in Riverside County, California, and described in 1933 by Esper S. Larsen and Kingsley Charles Dunham , who named the mineral after Cecil Edgar Tilley (1894–1973) to honor his contributions to the study of metamorphic rocks.

Type material of the mineral has been deposited at Harvard University in Cambridge / Massachusetts (Register No. 97301) and the National Museum of Natural History in Washington, DC (Register No. 97246).

classification

Already in the outdated 8th edition of the mineral classification according to Strunz , tilleyite belonged to the department of " group silicates (sorosilicates)", where together with cuspidin and rustumite as well as in the appendix with foshallasite (discredited in 2006) and suolunite ( solanite ) he created the "cuspidin-tilleyite Group "with the system no. VIII / B.06 .

In the Lapis mineral directory according to Stefan Weiß, which, out of consideration for private collectors and institutional collections, is still based on this old form of Karl Hugo Strunz's system , the mineral was given the system and mineral number. VIII / C.09-20 . In the “Lapis system”, this also corresponds to the “Group silicates” section, where Tilleyit, together with Aklimait , Cuspidin, Fukalith , Jaffeit , Killalait , Rusinovit and Suolunit, forms an independent but unnamed group (as of 2018).

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies tilleyite in the group of "group silicates". However, this is further subdivided according to the structure of the silicate groups, so that the mineral can be classified in the sub-section “Si 2 O 7 groups with additional anions ; Cations in octahedral [6] and greater coordination ”can be found, where it is the only member of the unnamed group 9.BE.82 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , classifies the tilleyite in the more finely subdivided division of "Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O". Here he is together with Killalait as the namesake of the " Tilleyit-Killalait Group " with the system no. 56.02.09 and the other member foshallasite within the sub-section “Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4] coordination”.

Crystal structure

Tilleyite crystallizes monoclinically in the space group P 2 1 / a (space group no. 14, position 3) with the lattice parameters a  = 15.11  Å ; b  = 10.24 Å; c  = 7.58 Å and β = 105.2 ° and 4 formula units per unit cell . Template: room group / 14.3

Education and Locations

Tilleyite is formed by contact metamorphism in the zone between volcanites and limestone at low pressure and high temperature. The accompanying minerals include calcite , fluorite , gehlenite , grossular , merwinite , spurrite , thaumasite , vesuvianite and wollastonite .

As a rare mineral formation, Tilleyite has so far (as of 2019) only been found at a few sites, with around 20 sites documented so far. Besides its type locality Crestmore the mineral in the United States took place among other things still in a quarry on Sky Blue Hill in California, at Iron Mountain District No. 2 in. Sierra County New Mexico, as well as an unnamed skarn - deposit in the Christmas Mountains in Brewster County and the Marble Canyon Mine in Culberson County , Texas.

Tilleyit was also found in Redcap Creek Skarn between Chillagoe and Herberton in the Australian Tablelands region , at some sites on Honshū in Japan, near Flekkeren in the Norwegian province of Telemark , near Alba and Hunedoara in Romania, on the Lower Tunguska near Anakit in Siberia , at Ol Doinyo Lengai in northern Tanzania as well as at Kilchoan on the Ardnamurchan Peninsula and Camas Mor on the Isle of Muck in the United Kingdom.

See also

literature

  • Esper S. Larsen, Kingsley C. Dunham: Tilleyite, a new mineral from the contact zone at Crestmore, California . In: The American Mineralogist . tape 18 , no. 11 , 1933, pp. 469–473 (English, rruff.info [PDF; 270 kB ; accessed on December 29, 2019]).

Web links

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

Individual evidence

  1. ↑ 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.  583 (English).
  2. ^ David Barthelmy: Tilleyite Mineral Data. In: webmineral.com. Retrieved December 29, 2019 .
  3. ↑ a b c d Tilleyite . 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; 76  kB ; accessed on December 29, 2019]).
  4. ↑ a b c d e Tilleyite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 29, 2019 .
  5. ↑ Catalog of Type Mineral Specimens - T. (PDF 87 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed December 29, 2019 .
  6. ↑ 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 .
  7. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1816 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed December 29, 2019 .
  8. ↑ Localities for Tilleyite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 29, 2019 .
  9. ↑ Find location list for Tilleyit at the Mineralienatlas and at Mindat , accessed on December 29th.