Vicanite- (Ce)

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Vicanite- (Ce)
General and classification
other names

IMA 1991-050

chemical formula (Ca, REE, Th) 15 Fe 3+ (SiO 4 ) 3 (Si 3 B 3 O 18 ) (BO 3 ) (As 5+ O 4 ) (As 3+ O 3 ) x (NaF 3 ) 1-x F 7 • 0.2H 2 O with x = 0.4
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.AJ.35 ( 8th edition : VIII / B.33)
54.03.01.01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-pyramidal; 3 m
Room group (no.) R 3 m (No. 160)
Lattice parameters a  = 10.8112 (2)  Å ; c  = 27.3296 (12) Å
Formula units Z  = 3
Physical Properties
Mohs hardness 5 to 6
Density (g / cm 3 ) measured:> 4.2; calculated: 4.73
Cleavage no
Break ; Tenacity clamshell; brittle
colour yellowish green
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.757
n ε  = 1.722
Birefringence δ = 0.035
Optical character uniaxial negative

Vicanite- (Ce) is a very rarely occurring mineral from the mineral class of " silicates and germanates ". It crystallizes in the trigonal crystal system with the chemical composition (Ca, REE, Th) 15 Fe 3+ (SiO 4 ) 3 (Si 3 B 3 O 18 ) (BO 3 ) (As 5+ O 4 ) (As 3+ O 3 ) x (NaF 3 ) 1-x F 7 • 0.2H 2 O with x = 0.4. The elements calcium , thorium and rare earth metals (REE) indicated in the round brackets can represent each other in the formula ( substitution , diadochy), but are always in the same proportion to the other components of the mineral.

The name appendix - (Ce) was given to the mineral due to its significant content of the rare earth metal cerium of up to 19.2%.

Vicanite- (Ce) rarely forms well-developed, prismatic crystals up to about 0.3 millimeters in size. It is mostly found in the form of irregular grains or granular aggregates .

Special properties

The mineral is considered due to its thorium content % and various rare earth metals, some of which isotopes of up to 9 radioactively are as highly radioactive. Taking into account the natural decay series or any decay products present, the specific activity is given as 4.069 k Bq / g (for comparison: natural potassium 0.0312 kBq / g).

Etymology and history

Vicanit was discovered for the first time in Tre Croci , a district of Vetralla near the Vico in the Italian province Viterbo and described in 1995 the mineral after the near by Adriana Maras, GC Parodi, G. Della Ventura and D. Without Stetter, type locality lying Named lake.

classification

Already in the outdated, but partly still in use 8th edition of the mineral systematics according to Strunz , the vicanite (Ce) belonged to the mineral class of "silicates and germanates" and there to the department of "island silicates with non-tetrahedral anions (Neso subsilicates)", where he together with Hundholmenit- (Y) , Melanocerit- (Ce) , Okanoganit- (Y) , Tritomit- (Ce) and Tritomit- (Y) formed the unnamed group VIII / B.33 .

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 the Vicanite (Ce) in the category of "Island silicates (Nesosilicates)". This is further subdivided according to the possible presence of further anions and the coordination of the cations involved , so that the mineral can be divided into corners according to its composition in the subsection “ Island silicates with BO 3 triangles and / or B [4] , Be [4] tetrahedra with SiO 4 "can be found, where it is named after the" Vicanit group "with the system no. 9.AJ.35 and the other members Hundholmenit- (Y), Okanoganit- (Y) and Proshchenkoit- (Y) .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Vicanite- (Ce) to the class of "Silicates and Germanates" and there in the department of "Island silicates: borosilicates and some beryllosilicates with (BO 3 )". Here he is together with Hundholmenit- (Y) and Proshchenkoit- (Y) in the " Vicanitgruppe " with the system no. 54.03.01 to be found in the subsection " Island silicates: borosilicates and some beryllosilicates".

Education and Locations

Vicanite- (Ce) forms in miarolithic cavities in ejecta ceilings with a syenitic composition.

In addition to its type locality Tre Croci, Vicanite- (Ce) could only be found at Le Carcarelle and Castellaccio di Petrignano near Vetralla and the municipality of Capranica, which is also near Lake Vica, and in the Alban Mountains in the Italian region of Lazio (as of 2013).

Crystal structure

Vicanite- (Ce) crystallizes trigonal in the space group R 3 m (space group no. 160) with the lattice parameters a  = 10.8112 (2)  Å and c  = 27.3296 (12) Å as well as 3 formula units per unit cell .

Precautions

Due to the strong radioactivity of the mineral, mineral samples from Vicanite (Ce) should only be kept in dust- and radiation-proof containers, but especially never in living rooms, bedrooms or work rooms. Absorption into the body ( incorporation , ingestion ) should also be prevented in any case and, for safety, direct body contact should be avoided and face masks and gloves should be worn when handling the mineral.

See also

literature

  • A. Maras, GC Parodi, G. Della Ventura, D. Ohnenstetter: Vicanite- (Ce): a new Ca-Th-REE borosilicate from Vico volcanic district (Latium, Italy). In: European Journal of Mineralogy. Volume 7 (1995), pp. 439-446
  • John L. Jambor , Jacek Puziewicz, Andrew C. Roberts: New Mineral Names. In: American Mineralogist. Volume 80 (1995), pp. 1328-1333 ( PDF 686 kB ; Vicanite- (Ce) p. 3)
  • Paolo Ballirano, Athos Callegari, Franca Caucia, Adriana Maras, Fiorenzo Mazzi, Luciano Ungaretti: The crystal structure of vicanite- (Ce), a borosilicate showing an unusual (Si 3 B 3 O 18 ) 15− polyanion. In: American Mineralogist. Volume 87 (2002), pp. 1139–1143 ( PDF 611.4 kB )

Web links

Individual evidence

  1. ↑ a b c d e Paolo Ballirano, Athos Callegari, Franca Caucia, Adriana Maras, Fiorenzo Mazzi, Luciano Ungaretti: The crystal structure of vicanite- (Ce), a borosilicate showing an unusual (Si 3 B 3 O 18 ) 15− polyanion . In: American Mineralogist. Volume 87 (2002), pp. 1139–1143 ( PDF 611.4 kB )
  2. ↑ a b c d Webmineral - Vicanite- (Ce)
  3. ↑ a b Mindat - Vicanite- (Ce)
  4. ↑ Find location list for Vicanit- (Ce) in the Mineralienatlas and in Mindat