Brannerite

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Brannerite
Brannerite-38635.jpg
Weathered, but fully developed Brannerite crystal from the "Dieresis Mine", El Cabril , Córdoba, Andalusia, Spain (size: 6.1 cm × 4.2 cm × 3.7 cm)
General and classification
other names

Cordobaite

chemical formula
  • UTi 2 O 6
  • (U, Ca, Y, Ce) (Ti, Fe) 2 O 6
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.05 ( 8th edition : IV / D.22)
03/08/04/01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / m (No. 12)Template: room group / 12
Lattice parameters a  = 9.81  Å ; b  = 3.77 Å; c  = 6.92 Å
β  = 119.0 °
Formula units Z  = 2
Physical Properties
Mohs hardness 4.5 to 5.5
Density (g / cm 3 ) measured: 4.2 to 5.43; calculated: [5.20]; synthetic UTi 2 O 6 : 6.37
Cleavage not defined
Break ; Tenacity shell-like
colour black, brownish-olive green, yellow-brown to yellow
Line color dark greenish brown to yellowish brown
transparency opaque, translucent brownish-red in thin layers
shine Glass gloss when fresh, otherwise pitch or resin-like to matt
radioactivity very strong
Crystal optics
Refractive index n  = 2.23 to 2.3
Birefringence none, as isotropicized by radioactivity

Brannerite is a rather rare mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the monoclinic crystal system with the idealized composition UTi 2 O 6 , so it is chemically a uranium - titanium oxide. Since uranium by naturally formed in Brannerit but usually small amounts of calcium , yttrium and / or cerium or small amounts of titanium by iron diadoch replaced are, the formula is often also with (U, Ca, Y, Ce) (Ti, Fe) 2 O 6 indicated.

Brannerite is generally opaque and only reddish translucent in thin layers and splinters. It only forms indistinct, prismatic crystals , which, however, can be up to 30 centimeters in size. However, it is mostly found in the form of rounded grains and massive aggregates of black, brownish-olive-green, yellow-brown to yellow in color with dark-greenish-brown to yellowish-brown streak color . Fresh mineral samples have a pitch -like to glass-like gloss , which over time changes to a resin-like gloss due to weathering, until the samples finally become matt.

Etymology and history

Brannerite was first discovered near Kelley Gulch , about 14 miles northwest of Stanley in Custer County , Idaho. The mineral was described in 1920 by Frank L. Hess and Roger C. Wells, who named it after the American geologist and former President of Stanford University (California) John Casper Branner (1850-1922).

Type material of the mineral is in the National Museum of Natural History in Washington DC in the USA under the catalog no. 105793 and 114997 kept.

classification

In the now obsolete, but still common 8th edition of the mineral classification by Strunz the Brannerit to the department of the part ": oxygen = 1: oxides with the molar ratio metal 2 (MO 2 and related compounds)" where he together with Orthobrannerit and Thorutit the "Brannerit series" with the system no. IV / D.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 assigns Brannerite to the division of "Oxides with the molar ratio of metal: oxygen = 1: 2 and comparable". However, this is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral is classified in the sub-section “With large (± medium-sized) cations; Layers of edge-linked octahedra "can be found where it also forms the" Brannerite-Orthobrannerite group " 4.DH.05 together with orthobrannerite and thorutite .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Brannerite to the mineral class of "oxides and hydroxides" in the division of "multiple oxides with Nb, Ta and Ti". Here it can be found together with thorutite in the unnamed group 08.03.04 within the subsection “Multiple oxides with Nb, Ta and Ti and the formula A (B 2 O 6 )”.

Crystal structure

Brannerite crystallizes monoclinically in the space group C 2 / m (space group no. 12) with the lattice parameters a  = 9.81  Å ; b  = 3.77 Å; c  = 6.92 Å and β = 119.0 ° and 2 formula units per unit cell . Template: room group / 12

properties

The mineral is very radioactive due to its uranium content of up to 33.5% . Taking into account the proportions of the radioactive elements in the idealized empirical formula as well as the subsequent decays of the natural decay series, a specific activity of about 60.221 k Bq / g is specified for the mineral (for comparison: natural potassium 0.0312 kBq / g). The quoted value can vary significantly depending on the mineral content and the composition of the levels; selective enrichment or depletion of the radioactive decay products is also possible and changes the activity.

Due to its radioactivity, Brannerite is mostly completely metamictic , i.e. its crystal structure was destroyed by its own ionizing radiation .

Modifications and varieties

Absit is a name that is no longer in use for a ThO 2 -containing variety of Brannerit.

Education and Locations

Tabular, twinned brannerite crystals from the uranium deposit in the Upper Palatinate Forest (size: 3.5 × 2.5 × 1.8 cm)

Brannerit either forms primarily in granitic pegmatites and granitic gneisses , silicified conglomerate and hydrothermal quartz - and calcite - wires or found detritisch in placer deposits . The accompanying minerals include apatite , gold , rutile , uraninite , xenotime and zircon .

As a rather rare mineral formation, Brannerite can sometimes be abundant at different sites, but overall it is not very common. Around 200 sites are known to date (as of 2013). In addition to its type locality Kelley Gulch, the mineral was found in several locations in Idaho as well as on Bokan Mountain ( Prince of Wales Island ) in Alaska, in the Swisshelm Mountains ( Cochise County ) in Arizona, and at several locations in Colorado , California , Nevada , New Mexico, and Washington can be found.

In Germany, Brannerite has only been found in the Müllenbach uranium deposit near Baden-Baden in Baden-Württemberg, the Mähring uranium deposit and in the Wölsendorfer fluorite mining area in Bavaria.

In Austria, the mineral could be found in the area around Friesach and Hüttenberg , in the Hohe Tauern from Carinthia to Salzburg as well as near Oberdorf in the Lamingtal and near Eisenerz in Styria .

In Switzerland, brannerite was found on the Mürtschenalp in the Murgtal ( Canton of Glarus ) and in the Vorderrheintal (Graubünden), at Augstchamm in the Weisstannental (St. Gallen), in Iragna (Ticino) as well as in the Lengenbach mine in the Binn valley and at Tête des Econduits am Mont Chemin in the canton of Valais .

Other locations are among others in Argentina, Australia, Belgium, Bolivia, Brazil, China, Finland, France, Guyana, India, Italy, Japan, Canada, Kazakhstan, Kyrgyzstan, Morocco, Mongolia, Namibia, Norway, Poland, Russia, Zambia , Sweden, Slovakia, Spain, South Africa, the Czech Republic, Ukraine, Hungary and the United Kingdom (Great Britain).

use

When locally accumulated, brannerite occasionally serves as uranium ore along with other uranium minerals .

Precautions

Due to its high level of radioactivity , samples of Brannerit should only be kept in dust-tight and radiation-proof containers and stored away from humans and animals. Ingestion into the body ( incorporation ) and direct body contact should be avoided. When handling the mineral, safety clothing, at least in the form of a face mask and gloves, must be worn.

literature

Web links

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

Individual evidence

  1. ↑ a b IMA / CNMNC List of Mineral Names; February 2013 (PDF 1.3 MB)
  2. ↑ 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.  221 .
  3. ↑ a b Webmineral - Brannerite
  4. ↑ a b c d e Brannerite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 72.4 kB )
  5. ↑ Mindat - Brannerite
  6. ↑ 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 .
  7. ↑ Old mineral names and synonyms at indra-g.at
  8. ↑ Mineralienatlas : Absit
  9. ↑ Mindat - Number of localities for Brannerite
  10. ↑ Find location list for Brannerite at the Mineralienatlas and at Mindat