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 of Ca6 [( OH) 2 | Si6O17 ] is therefore a calcium silicate with additional hydroxide. Structurally, it belongs to the chain and belt silicates ( Inosilikaten ).
Xonotlite usually develops fibrous to acicular crystals to about two centimeters in length, which are stretched parallel to the b axis and are arranged in radialstrahligen, rosette-shaped or spherical mineral aggregates that have a pearl - like luster to fat. Also, foliated and massive aggregates were observed. In its pure form Xonotlite is colorless and transparent. However, it appears mostly white and by foreign admixtures he occasionally takes a bluish gray or light pink to reddish color to the transparency decreases correspondingly by multiple refraction due to polycrystalline training.
With a Mohs hardness of 6 to 6.5 Xonotlite is one of the hard minerals that are similar as the reference mineral orthoclase (6 ) can barely scratched with a steel file. However Xonotlite is brittle and breaks in splintery to uneven mechanical loading, which caused uneven to conchoidal fracture surfaces.
Etymology and history
Was first discovered the mineral in a mine in Tetela de Xonotla (also de Tonatla ) in Puebla, Central Mexico and described in 1866 by Carl Rammelsberg, who named it after its type locality, but first in the spelling Xonaltit. 1875 corrected Rammelsberg the mineral name to the present spelling Xonotlite.
In the outdated, but partly still in use 8th edition of the mineral classification by Strunz the Xonotlite belonged to the department of " chain silicates and phyllosilicates ( inosilicates ) ", where he was named. , The " Xonotlitgruppe " with the System No. Formed VIII/F.21 and the other members hillebrandite, Nekoit and Scawtite.
The 9th edition valid since 2001 and of the International Mineralogical Association (IMA ) used the Strunz'schen Mineral classification assigns the Xonotlite also included in the department's " chain and chain silicates ( inosilicates ) ". However, this is further divided according to the structure of the chains or belts so that the mineral " chain and chain silicates with 3- periodic single and multiple chains " can be found according to its construction in the subdivision where it is the only member of the unnamed group 9.DG.35 forms.
The mainly common in English-speaking classification of minerals according to Dana assigns the Xonotlite in the class of " silicates and Germanates " there, however, in the department of " chain silicates: Double unbranched chains, W = 2". Here he is with Zorite, Eudidymit, Epididymit, Yuksporit, Haineaultit and Chivruaiit in the "P = 3" with the system no. 66.03.01 within the subdivision " chain silicates: Double unbranched chains, W with chains P = 2 > 2 " to find.
Modifications and varieties
From Xonotlite two varieties are known. Both were first described as a distinct minerals, but later discredited after it was found that they were identical with Xonotlite.
" Jurupait " was described in 1921 by Arthur Starr Eakle who found the mineral in a quarry at Crestmore in Riverside County in the U.S. state of California, more precisely in the Crestmore Hills, which are part of the Jurupa Mountains. HFW Taylor 1921 compared with samples from Jurupait Xonotlite and was able to demonstrate that both minerals are identical. Minor deviations in the lattice parameters, he led back to a partial substitution of calcium by magnesium. The mineral name Jurupait was therefore discredited and has been the synonym of Xonotlite.
" Eakleit " was first described in 1917 by Esper Larsen Signius as a separate mineral from California, but corrected his description in 1923, after he was made aware by Waldemar Theodore Schaller that the new mineral was chemically identical to the Xonotlite briefly described above. Comparative analyzes with different materials of Xonotlite and Eakleit confirmed the identity and the mineral name Eakleit was discredited.
Education and Locations
Xonotlite forms in kontaktmetamorphen deposits within limestone, serpentinite and metavolcanic rocks. Accompanying minerals among other Apophyllite, diopside, Klinoedrit, laumontite, stilbite, thaumasite, tobermorite and wollastonite may occur.
A rare mineral formation Xonotlite could be detected only in a few localities, where so far (as of 2013) are nearly 100 localities known as. Apart from its type locality Tetela de Xonotla the mineral still came to light in several mines in Tetela de Ocampo, Puebla and in the pit " Guadalupe " in Pachuca de Soto, Hidalgo, Mexico.
The only known locality in Germany in a closed quarry at Glass Mountain in low - Beersbach in Hesse.
Other localities lie including 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).
Xonotlite crystallizes in the monoclinic space group P2 / a ( Raumgruppen-Nr. 13) with the lattice parameters a = 17.03 Å; b = 7.36 Å; c = 7.01 Å and 90.3 ° β = and two formula units per unit cell.