Brannockite

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Brannockite
General and classification
other names

IMA 1972-029

chemical formula KSn 4+ 2 Li 3 Si 12 O 30
Mineral class
(and possibly department) 		Silicates and germanates - ring silicates
System no. to Strunz
and to Dana 		9.CM.05 ( 8th edition : VIII / E.22)
63.02.01a.01
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Space group P 6 / mcc (No. 192)Template: room group / 192
Lattice parameters a  = 10.0167  Å ; c  = 14.2452 Å
Formula units Z  = 2
Frequent crystal faces {001}, subordinate {100}, {110}, {114}
Twinning often, not externally visible
Physical Properties
Mohs hardness not determined
Density (g / cm 3 ) measured: 2.98; calculated: 3.08
Cleavage is missing
Break ; Tenacity brittle
colour colorless
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.567
n ε  = 1.566
Birefringence δ = 0.001
Optical character uniaxial negative
Other properties
Special features bright, bluish white fluorescence under short-wave UV light

The mineral brannockite is a very rarely occurring ring silicate from the milarite group within the mineral class of silicates and germanates with the idealized chemical composition KSn 4+ 2 Li 3 Si 12 O 30 . It crystallizes in the hexagonal crystal system and develops aggregates of colorless, platy crystals a few millimeters in size.

Brannockite is found in late hydrothermal areas of alkali-rich pegmatites in which lithium and tin have accumulated . In addition to its type locality , the Foot Mine in Kings Mountain District, Cleveland County , North Carolina , USA , Brannockit has only been found at one other location in Washington , USA.

Etymology and history

Brannockite was discovered in 1968 by C. Hudgins of Marion, North Carolina, in the Foot Mine, a lithium-rich granite pegmatite. He donated a sample to the Smithsonian Institution's National Museum of Natural History , where it was scientifically examined by John S. White and his coworkers and characterized as a Li-Sn analog by Osumilith . They named the mineral after the chemist and mineral collector Dr. Kent Combs Brannock (1923-1973) from Kingsport , Tennessee , who was instrumental in the description of numerous minerals from the Foot Mine.

The discovery was published five years later in The Mineralogical Record , a journal that John S. White himself founded in 1970.

classification

Already in the outdated, but still in use 8th edition of the mineral classification according to Strunz , Brannockit belonged to the division of " ring silicates (cyclosilicates)", where it was found together with Almarudit , Armenit , Berezanskit , Chayesit , Darapiosit , Dusmatovit , Eifelit , Emeleusit , Faizievit , Merrihueit , Milarite , Oftedalite , Osumilite , Osumilite- (Mg) , Poudretteite , Roedderite , Shibkovite , Sogdianite , Sugilite , Trattnerite , Yagiite and Yakovenchukite- (Y) the " Milarite-Osumilite Group " with the system no. VIII / E.22 .

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 Brannockit in the "ring silicates" section. This is, however, further subdivided according to the structure of the rings, so that the mineral can be found in the sub-section "[Si 6 O 18 ] 12− -six double rings" according to its structure . With Almarudit, Armenit, Berezanskit, Chayesit, Darapiosit, Dusmatovit, Eifelit, Friedrichbeckeit , Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteite, Roedderit, Shibkovite, Sogdianite, Sugilite and, Trianite, belongs to the Sugilite " Milaritgruppe " with the system no. 9.CM.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Brannockite to the class of "silicates and Germanates", but there in the more finely divided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.

Chemism

Brannockite is the lithium-tin analog of Osumilith and the measured composition from the type locality is [12] K [6] Sn 2 [4] Li 3 [4] Si 12 O 30 , with the coordination number of the respective position in square brackets is indicated in the crystal structure.

Brannockite forms mixed crystals with Berezansite, Sogdianite and, to a lesser extent, sugilite, which results from the replacement of Sn 4+ by Ti 4+ , Zr 4+ and Hf 4+ and the coupled incorporation of [6] Fe / Al 3+ and [9] Na + expresses.

Crystal structure

Brannockite crystallizes in the hexagonal crystal system in the space group P 6 / mcc (space group  no.192 ) with the lattice parameters a = 10.0167  Å and c  = 14.2452 Å as well as two formula units per unit cell .  Template: room group / 192

Brannockite is isotypic to milarite , ie it crystallizes with the same structure as milarite. The 12-fold coordinated C-position is fully occupied with potassium (K + ) and the 9-fold coordinated B-position is vacant. Tin (Sn 4+ ) occupies the 6-fold coordinated A position. The tetrahedrally coordinated T2 position contains only lithium (Li + ). The T1 position, which builds up the 6 double rings, only contains silicon (Si 4+ ).

Education and Locations

Brannockite forms in the late hydrothermal phase of alkali-rich pegmatites.

Brannockit has only been documented at two sites worldwide (as of 2016).

At its type locality , the Foot Mine in Kings Mountain District, Cleveland Co. , North Carolina , USA , brannokit is found in miaroles and cracks. It occurs here together with quartz , albite , the multiple chain silicate bavenite , pyrite , the hydroxide tetrawickmanite and titanite .

This very mineral-rich site is the type locality of 13 minerals (as of 2016). Brannockite is the only mineral of the milarite group there.

The second documented location is an alkali-rich granite from the Golden Horn batholith at Liberty Bell / Washington Pass in Okanogan County , Washington , USA . Brannockite occurs here with the Li-Zr-Osumilite Sogdianite and the Li-Na-Zr-6-double chain silicate zektzerite , which was first described here.

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s JS White, JE Arem, JA Nelen, PB Leavens, RW Thomssen: Brannockite, a new tin mineral . In: The Mineralogical Record . tape 4 , March 1973, p. 73–76 ( rruff.info [PDF; 2.1 MB ; accessed on August 30, 2018]).
  2. ↑ a b c d e f g h i j k l Michael Fleischer: New Mineral Names . In: The American Mineralogist . tape 58 , 1973, p. 1111–1115 ( rruff.info [PDF; 572 kB ; Retrieved August 30, 2018] Brannockite, p. 1111).
  3. ↑ a b c d e Thomas Armbruster, Roland Oberänsli: Crystal chemistry of double-ring silicates: Structures of sugilite and brannockite . In: The American Mineralogist . tape 73 , 1988, pp. 595–600 ( rruff.info [PDF; 1.1 MB ; accessed on August 30, 2018]).
  4. ↑ Webmineral - Brannockite (English)
  5. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  6. ↑ a b Brannockite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 60  kB ; accessed on August 30, 2018]).
  7. ↑ a b c MB Raschke, EJD Anderson, J. Allaz, H. Friis, JR Smyth, R. Tschernich, R. Becker: Crystal chemistry of brannockite, KLi 3 Sn 2 Si 12 O 30 , from a new occurrence in the Golden Horn batholith, Washington State, USA . In: European Journal of Mineralogy . tape 28 , no. 1 , March 2016, p. 153–161 , doi : 10.1127 / ejm / 2015 / 0027-2477 ( summary ).
  8. ↑ Wendell E. Wilson: The Mineralogical Record: John S. White. Retrieved August 30, 2018 .
  9. ^ Foote Lithium Co. Mine (Foote Mine), Kings Mountain District, Cleveland Co., North Carolina, USA
  10. ↑ Washington Pass, Golden Horn Batholith, Okanogan Co., Washington, USA