Cetineite

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Cetineite
Cetineite-203798.jpg
Ruby-red, tufted aggregate of needle-like cetineite from the type locality "Le Cetine di Cotorniano Mine" near Chiusdino in Italy
General and classification
other names

IMA 1986-019

chemical formula (K, Na) 3 + x (Sb 2 O 3 ) 3 (SbS 3 ) (OH) x  • 2.4H 2 O (with x ~ 0.5)
Mineral class
(and possibly department) 		Sulfides and sulfosalts
System no. to Strunz
and to Dana 		2.MA.05 ( 8th edition : II / F.11)
02.13.03.01
Similar minerals Kermesite , sarabauite , zeolites (similarity in chemical behavior)
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol hexagonal-pyramidal 6
Lattice parameters a  = 14.23  Å ; c  = 5.57 Å Please complete the source as an individual reference!
Physical Properties
Mohs hardness 3.5
Density (g / cm 3 ) 4.21 (calculated)
Cleavage good after {1000}
colour yellow-orange, orange-red
Line color orange
transparency transparent to translucent
shine Resin gloss
radioactivity hardly measurable
Crystal optics
Optical character uniaxial positive
Pleochroism weak; orange-orange-brown

Cetineite is a very rarely occurring mineral from the mineral class of " sulfides and sulfosalts ". It crystallizes in the hexagonal crystal system with the idealized composition NaK 5 Sb 14 S 6 O 18  • 6H 2 O, more precisely (K, Na) 3 + x (Sb 2 O 3 ) 3 (SbS 3 ) (OH) x  • 2.4H 2 O (with x ~ 0.5).

The crystals of the natural cetineite are unevenly structured and disordered, often clusters of dark gray, orange, violet-brown to purple-red crystal needles with a maximum length of 3 mm can be found. Depending on the composition or production method, the crystal structure , shape and color of the cetineite minerals can vary greatly. Mostly one finds hexagonal structures.

Chemism

The general molecular formula of cetineite is:

A 6 [Sb 12 O 18 ] [Sb X 3 ] 2  · (6 -  mx  y ) H 2 O  ·  x [ B m + (OH) m ] ·  y  Ø , where

Etymology and history

Cetineit was first discovered in 1986 in the Le Cetine mine near Chiusdino in the Italian province of Siena . The mineral was described in 1987 by C. Sabelli and G. Vezzalini, who named it after its type locality .

classification

In the now outdated, but still in use 8th edition of the mineral classification according to Strunz , the cetineite belonged to the mineral class of "sulfides and sulfosalts" and to the department of "non-metallic sulfides", where it formed an independent group together with kermesite , ottensite and sarabauite .

The 9th edition of Strunz's mineral systematics, valid since 2001 and used by the International Mineralogical Association (IMA), also assigns cetineite to the class of “sulfides and sulfosalts (sulfides, selenides, tellurides, arsenides, antimonides, bismuthides, sulfarsenites, sulfantimonites , Sulfbismuthite) ”and there in the section“ Oxysulfosalze ”. Here the mineral is in the sub-section "A Oxysulfosalts of alkalis and alkaline earths", where together with ottensite it forms group 2.MA.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the cetineite to the class of "sulfides and sulfosalts" and there into the department of "sulfide minerals". Here it can also be found together with Ottensite in the unnamed group 02.13.03 within the subdivision of " Sulphides - including selenides and tellurides - oxysulphides ".

Education and Locations

Cetineite is formed by the deposition of antimony in silicate-rich evaporites . Accompanying minerals include mopungite and senarmontite .

In total, Cetineite has so far (as of 2011) been found at around 10 sites. In addition to its type locality “Le Cetine di Cotorniano Mine” near Chiusdino, the mineral joined the “Tafone Mine” and the “Macchia Casella Mine” near Manciano as well as the “Su Suergiu Mine” near Villasalto and the “Corti Rosas Mine” in Italy Ballao in the province of Cagliari in Sardinia.

Other sites are Qinglong (Qianxinan) in the province of Guizhou and the province of Hunan in China and the Goesdorf antimony mine in the Luxembourg canton of Wiltz .

Synthetic manufacture

Synthetic cetineites show interesting physical and structural properties and have so far only been able to be produced with great effort and in small quantities.

The hydrothermal synthesis is used for this. Here natural development conditions are simulated, i.e. high temperature and high pressure . The cetineites then form through self-organization in the form of individual small needles, but templates must be used if you want to obtain certain crystal shapes and properties.

Crystal structure

The crystal class of cetineite is hexagonal-pyramidal with the symmetry description 6 (according to Hermann and Mauguin ) and the lattice parameters a  = 14.23  Å and c  = 5.57 Å.

Under certain reaction conditions, nanoporous cetineite crystals form:

  • Hexagonal structure of photo-semiconductor tubes with a diameter of approx. 7 Å, which run along the length of the crystal.
  • Inside this photo-semiconducting host structure of tubes are embedded "guests", that is cations like Na + or K + , as well as water molecules.
  • In terms of their ability to exchange ions and absorb / release water, the cetineites are very similar to the zeolites with the difference that zeolites are ion conductors, whereas cetineites are electron conductors.

Without templates, thermodynamically more stable cetineites are created, which are neither porous nor semiconducting and are more related to the natural cetineites.

use

The production and properties of cetineites of different compositions are currently being researched, but their use in microelectronics , microsensors and catalysis is no longer far off.

See also

Individual evidence

  1. ↑ a b Handbook of Mineralogy - Cetineite (English, PDF 61.6 kB)
  2. ↑ IMA / CNMNC List of Mineral Names - Cetineite (English, PDF 1.8 MB; p. 50).
  3. ↑ Mindat - Cetineite (English).
  4. ^ Mineral Atlas: Cetineite .

literature

  • C. Sabelli, G. Vezzalini: Cetineite, a new antimony oxide-sulfide mineral from Cetine mine, Tuscany, Italy , in: Neues Jahrbuch der Mineralogie ,monthshefte (1987), pp. 419-425

Web links

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