Agrellite

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Agrellite
Museo di mineralogia, pietre fluorescenti, agrellite 3.JPG
Fluorescent agrellite exhibited in the Museo di Storia Naturale (Natural History Museum) in Florence
General and classification
other names

IMA 1973-032

chemical formula NaCa 2 [F | Si 4 O 10 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DH.75 ( 8th edition : VIII / H.15)
01/07/01/04
Similar minerals Zinnwaldite
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic-pinacoidal 1
Space group P 1
Lattice parameters a  = 7.76  Å ; b  = 18.95 Å; c  = 6.99 Å,
α  = 89.9 °; β  = 116.6 °; γ  = 94.3 °
Formula units Z  = 4
Physical Properties
Mohs hardness 5.5
Density (g / cm 3 ) 2.9
Cleavage Well
Break ; Tenacity uneven
colour gray-white to greenish
Line color White
transparency transparent to translucent
shine Glass gloss, matt to mother-of-pearl on the cleavage surfaces
Crystal optics
Refractive indices n α  = 1.567
n β  = 1.579
n γ  = 1.581
Birefringence δ = 0.014
Optical character biaxial negative
Axis angle 2V = 47 °
Other properties
Special features violet fluorescence

The mineral agrellite is a very rarely occurring chain silicate from the mineral class of " silicates and germanates ". It crystallizes in the triclinic crystal system with the chemical composition NaCa 2 [F | Si 4 O 10 ] and develops mostly long prismatic crystals up to about 10 cm in length, but also tabular mineral aggregates of gray-white to greenish color.

Etymology and history

Agrellite was first found in 1973 in the Kipawa complex of Témiscamingue in Canada and described in 1976 by J. Gittins, MG Brown and BD Sturman, who named the mineral after the English mineralogist Dr. Stuart Olof Agrell (1913-1996).

classification

In the meantime outdated 8th edition of the mineral classification by Strunz of agrellite still belongs to the department of " phyllosilicates (phyllosilicates)," where he met along Glagolevit and Mountainit formed a separate group.

Since the revision of Strunz's mineral system in the 9th edition , however, the mineral has been re-sorted into the subdivision of " Chain and band silicates with 4-periodic single chains, Si 4 O 12 ", where the unnamed group 9 is the only member . DH.75 forms.

The systematics of minerals according to Dana , which is common in the English-speaking world , also sorts the agrellite into the chain silicates section, but there into the subdivision “ with columnar or tube structures with columnar silicate units”, where it forms the unnamed group together with litidionite , fenaksite and manaksite 70.1.1 forms.

Crystal structure

Agrellite crystallizes triclinically in the space group P 1 with the lattice parameters a  = 7.76  Å ; b  = 18.95 Å; c  = 6.99 Å; α = 89.9 °; β = 116.6 ° and γ = 94.3 ° as well as four formula units per unit cell .

properties

Agrellite shows a light violet fluorescence under long-wave UV light and a dark violet fluorescence under short-wave UV light .

Education and Locations

Agrellite forms metamorphically in alkaline gneisses .

In addition to its type locality, the Kipawa complex in Canada, the mineral was found at around 10 sites worldwide (as of 2010), including in the Murun massif of the Aldan highlands (Eastern Siberia) and in the Chibinen on the Kola peninsula in Russia; on the Darai-Pioz Glacier in the Alai Mountains of Tajikistan as well as in the Wausau Plateau and in the Plutons near Stettin ( Wisconsin ) in the USA.

See also

literature

Web links

Commons : Agrellite  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 645 .
  2. ↑ Webmineral - Agrellite (English)
  3. ↑ a b c Agrellite at mindat.org (engl.)