Xonotlite

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Xonotlite
Xonotlite-Apophyllite-122280.jpg
Needle-spherical xonotlite on apophyllite from the "Wessels Mine", Hotazel , Kalahari , South Africa (size: 7.8 × 4.2 × 2.7 cm)
General and classification
other names
  • Xonaltite
  • Eakleit
  • Jurupait
chemical formula Ca 6 [(OH) 2 | Si 6 O 17 ]
Mineral class
(and possibly department) 		Silicates and germanates - chain and band silicates (inosilicates)
System no. to Strunz
and to Dana 		9.DG.35 ( 8th edition : VIII / F.21)
66.03.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 / a (No. 13, position 3)Template: room group / 13.3
Lattice parameters a  = 17.03  Å ; b  = 7.36 Å; c  = 7.01 Å
β  = 90.3 °
Formula units Z  = 2
Physical Properties
Mohs hardness 6 to 6.5
Density (g / cm 3 ) measured: 2.71 to 2.72; calculated: 2.71
Cleavage completely after {h01}
Break ; Tenacity uneven to shell-like; splintery
colour chalk white to bluish gray, light pink to reddish
Line color White
transparency translucent
shine Pearlescent, greasy luster
Crystal optics
Refractive indices n α  = 1.583
n β  = 1.585
n γ  = 1.595
Birefringence δ = 0.012
Optical character biaxial positive
Axis angle 2V = 50 ° (calculated)

Xonotlite is a rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition Ca 6 [(OH) 2 | Si 6 O 17 ], so it is a calcium silicate with additional hydroxide ions . Structurally it belongs to the chain and band silicates (inosilicates).

Xonotlite usually develops fibrous to needle-like crystals up to about two centimeters in length, which are stretched parallel to the b-axis [010] and arranged in radial, rosette-shaped or spherical mineral aggregates with a pearlescent to fat-like sheen . Flaky and tough aggregates were also observed. In its pure form, xonotlite is colorless and transparent. Due to the multiple refraction of light due to its polycrystalline formation, however, it usually appears white and due to foreign admixtures it occasionally takes on a bluish-gray or light pink to reddish color, whereby the transparency decreases accordingly.

With a Mohs hardness of 6 to 6.5, Xonotlite is one of the hard minerals that, like the reference mineral orthoclase (6), can just be scratched with a steel file . However, xonotlite is brittle and breaks in a splintery manner when exposed to uneven loads, with uneven to shell-like fracture surfaces.

Etymology and history

The mineral was first discovered in a mine near Tetela de Xonotla (also de Tonatla ) near Puebla in central Mexico and described in 1866 by Carl Rammelsberg , who named it after its type locality , but initially in the spelling Xonaltite . In 1875 Rammelsberg corrected the mineral name in the current spelling Xonotlit.

classification

In the outdated, but partly still in use, 8th edition of the mineral classification according to Strunz , the xonotlite belonged to the department of "chain silicates and band silicates (inosilicates)", where it was named after the "xonotlite group" with the system no. VIII / F.21 and the other members Hillebrandit , Nekoit and Scawtit .

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 classifies xonotlite in the category of "chain and band silicates (inosilicates)". This is, however, further subdivided according to the structure of the chains or bands, so that the mineral can be found according to its structure in the sub-section "Chain and band silicates with 3-periodic single and multiple chains", where it is the only member of the unnamed group 9.DG.35 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the xonotlite to the class of "silicates and Germanates", but there in the department of "chain silicates: double unbranched chains, W = 2". Here it is together with Zorit , Eudidymit , Epididymit , Yuksporit , Haineaultit and Chivruaiit in the " P = 3 " with the system no. 66.03.01 to be found in the subsection “Chain silicates: Double unbranched chains, W = 2 with chains P> 2”.

Modifications and varieties

Two varieties of Xonotlit are known. Both were initially described as separate minerals, but later discredited after they were found to be identical to xonotlite.

“Jurupait” was described in 1921 by Arthur Starr Eakle , who found the mineral in a quarry near Crestmore in Riverside County , California, more precisely in the Crestmore Hills, which are part of the Jurupa Mountains . HFW Taylor compared samples from Jurupait with Xonotlite in 1921 and was able to prove that both minerals are identical. He attributed slight deviations in the lattice parameters to a partial substitution of calcium by magnesium . The mineral name Jurupait was therefore discredited and has been a synonym of Xonotlite ever since.

"Eakleit" was initially described by Esper Signius Larsen in 1917 as an independent mineral from California, but corrected its description in 1923 after Waldemar Theodore Schaller made his attention to the fact that the new mineral was chemically identical to the xonotlite described shortly before. Comparative analyzes with different material from Xonotlite and Eakleit confirmed the identity and the mineral name Eakleit was discredited.

Crystal structure

Xonotlite crystallizes monoclinically in the space group P 2 / a (space group no. 13, position 3) with the lattice parameters a  = 17.03  Å ; b  = 7.36 Å; c  = 7.01 Å and β = 90.3 ° as well as two formula units per unit cell . Template: room group / 13.3

Education and Locations

Fibrous xonotlite (white) on epidote (Pb) (formerly hancockite ) from the "Franklin Mine", Franklin (New Jersey) , USA (field of view: 3 mm)
Spherical xonotlite on inesite from the "Wessels Mine", Hotazel , Kalahari , South Africa (size: 3.5 × 2.7 × 2.6 cm)

Xonotlite forms in contact metamorphic deposits within limestones , serpentinites and metavolcanic rocks. As accompanying minerals may include Apophyllit , diopside , Klinoedrit , Laumontit , Stilbit , thaumasite , tobermorite and wollastonite occur.

As a rare mineral formation, Xonotlite could only be detected at a few sites, whereby so far (as of 2013) almost 100 sites are known. In addition to its type locality Tetela de Xonotla, the mineral appeared in Mexico in several pits near Tetela de Ocampo in Puebla and in the “Guadalupe” mine near Pachuca de Soto in Hidalgo.

The only previously known site in Germany in a closed quarry on Glasberg near Nieder-Beerbach in Hesse.

Other locations include Australia, Bulgaria, Finland, Greenland, Iceland, Iraq, Ireland, Israel, Italy, Japan, Canada, New Zealand, Puerto Rico, Romania, Russia, Sweden, South Africa, the Czech Republic, the United Kingdom (UK) and the United States of America (USA).

See also

literature

  • C. Rammelsberg : About the xonaltite, a new water-containing calcium silicate, and the bustamite from Mexico , In: Journal of the German Geological Society , Volume 18 (1866), pp. 33-34 ( rruff.info PDF; 118.5 kB).
  • Arthur S. Eakle: Jurupaite - a new Mineral , In: American Mineralogist 1921, Volume 6, No. 7, pp. 107-109 ( minsocam.org PDF; 276.9 kB).
  • HFW Taylor: The identity of jurupaite and xonotlite , In: Mineralogical Magazine 1954, Volume 30, pp. 338-341 ( minersoc.org PDF; 564.3 kB).
  • Esper Signius Larsen: Eakleite, a new mineral from California , In: American Journal of Science 1917, Volume 4, Volume 43, pp. 464-465 doi: 10.2475 / ajs.s4-43.258.464 .
  • Esper Signius Larsen: The identity of Eakleite and Xonotlite , In: American Mineralogist 1923, Volume 10, pp. 181-182 ( minsocam.org PDF; 114.4 kB).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke, Stuttgart 1978, ISBN 3-432-82986-8 , pp. 733 (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. 541 .
  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Dörfler Verlag GmbH, Eggolsheim 2002, ISBN 978-3-89555-076-8 , p. 244 .

Web links

Commons : Xonotlite  - 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.  639 .
  2. ↑ Webmineral - xonotlite
  3. ↑ a b c Xonotlite. 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).
  4. ↑ a b c Mindat - Xonotlite
  5. ^ Johann Carl Buschmann: About the Aztec place names . Dogma, ISBN 978-3-95580-648-4 , pp. 188 ( available online in Google Book Search).
  6. ^ Albert Huntington Chester: A Dictionary of the Names of Minerals . 1st edition. John Wiley & Sons / Chapman & Hall, Ltd., New York / London 1896, p. 291 ( Textarchiv - Internet Archive - Ramm. Min. Ch. 880 = CF Rammelsberg: hand dictionary of the chemical part of mineralogy , Berlin 1841 and manual of mineral chemistry , Leipzig 1860, 2nd edition, 2nd volume 1875).
  7. ↑ Mindat - Number of localities for Xonotlit
  8. ↑ Find location list for xonotlite at the Mineralienatlas and at Mindat