Heftetjernit

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Heftetjernit
General and classification
other names

IMA 2006-056

chemical formula ScTaO 4
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DB.30 ( 8th edition : IV / D.16)
01/48/01/04
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 / c (No. 13)Template: room group / 13
Lattice parameters a  = 4.784  Å ; b  = 5.693 Å; c  = 5.120 Å
β  = 91.15 °
Formula units Z  = 2
Frequent crystal faces {100}
Physical Properties
Mohs hardness 4.5 (estimated in analogy to Ferberit)
Density (g / cm 3 ) 6.44 (calculated)
Cleavage very perfect after {010}
Break ; Tenacity uneven; brittle
colour deep dark brown, e.g. T. greenish brown; Normal interference colors and at most weak dispersion in transmitted light.
Line color dark brown with a reddish tone
transparency translucent to translucent
shine Diamond luster
Crystal optics
Refractive index n  = 2.23
Optical character biaxial, orientation unknown
Pleochroism weakly from brown with a reddish tinge to reddish brown

Heftetjernit is a very rarely occurring minerals from the mineral class of "oxides and hydroxides" with the chemical composition ScTaO 4 and is thus chemically seen a scandium - tantalum - oxide in the molar ratio of metal: oxygen = 1: 2.

Heftetjernite crystallizes in the monoclinic crystal system and has so far only been found in the form of elongated tabular crystals up to about 0.4 × 0.1 mm in size with a deep dark brown color in cavities in the albite .

The type locality of the mineral is the Cleavelandite - Amazonite - Pegmatite "Heftetjern" in Drangedal , Telemark , Norway , located 4.3 km northwest of Tørdal between Høydalen and Skarsfjell, where high quality amazonite has been mined since the early 1970s. This pegmatite, which is rich in Sc-containing or Sc-bearing minerals, is also the type locality for Agakhanovite- (Y) , Kristiansenite and Oftedalite as well as the still unnamed (OH) -dominant analogue of Gadolinite- (Y) .

Etymology and history

Heftetjernite was first observed in 2004 by the amateur mineralogist Roy Kristiansen while investigating a small albite specimen from the Heftetjern pegmatite. Heftetjernit was recognized by the International Mineralogical Association (IMA) in 2006 and first described in 2010 in the European journal of Mineralogy by Uwe Kolitsch , Roy Kristiansen, Gunnar Raade and Ekkehart Tillmanns . They named the mineral after its type locality, the pegmatite Heftetjern. The name of the pegmatite is explained as follows: The small lake near the quarry is a "tjern" (Norwegian for mountain lake or pond); “Tack” means to inhibit or delay. “Heftetjern” can roughly be translated as “ you are prevented from walking straight ahead in the landscape because you have to avoid the lake ”.

Type material of the mineral is in the collection of the Department of Geology, Naturhistorisk Museum in Oslo , Norway , under catalog no. 41726 kept.

classification

According to the 8th edition of the mineral systematics according to Strunz , which is outdated, but still in use , Heftetjernite with ferberite , hebnerite , sanmartinite and the now discredited wolframo-ixiolite would be the " wolframite series" with the system no. IV / D.16 form.

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 Heftetjernit in the category 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 medium-sized cations; "Is to find where it along with Ferberite, chains edge-sharing octahedra Huanzalait , Hübnerit, Krasnoselskit , Magnesiowolframit , Rossovskyit and Sanmartinit the" "with the system no. Wolframite group 4.DB.30 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , assigns Heftetjernit, in contrast to Strunz's systematics, to the class of "phosphates, arsenates, vanadates" and there in the department of "molybdates and wolframates". Here it is together with wolframite, ferberite, hebnerite and sanmartinite in the "wolframite series" with the system no. 48.01.01 to be found in the subsection of " Anhydrous molybdates and tungstates with A XO 4 ".

Chemism

The analysis of the stitching jernite of stitching tetras gave mean values ​​of 15.59% Sc 2 O 3 ; 6.93% SnO 2 ; 1.61% TiO 2 ; 3.02% MnO; 2.07% FeO; 53.58% Ta 2 O 5 and 14.25% Nb 2 O 5 . The empirical formula (Sc 0.64 Sn 0.13 Mn 0.12 Fe 0.08 Ti 0.06 ) Σ = 1.03 (Ta 0.69 Nb 0.30 ) Σ was calculated on the basis of four oxygen atoms = 0.99 O 4 , which has been simplified to (Sc, Sn, Mn, Fe, Ti) (Ta, Nb) O 4 . The ideal formula for the mineral, on the other hand, is ScTaO 4 , which requires levels of 23.79% Sc 2 O 3 and 76.21% Ta 2 O 5 .

As a result, mixed crystal formation is possible with the niob-dominant terminal link with the formula ScNbO 4, which has already been proven in nature but is not yet recognized as a mineral . Chemically , heftetjernite can be used as an Sc-dominant analogue of the Al 3+ -dominated alumotantite , AlTaO 4 , the Y-dominant minerals iwashiroite- (Y) and formanite- (Y) , both YTaO 4 , or the Mn-dominant tantalite- (Mn) , MnTa 2 O 5 , but they have completely different crystal structures.

Among the 19 scandium minerals recognized by the IMA today, Heftetjernite was the 11th chronologically described scandium phase and the world's first natural terrestrial scandium oxide.

Crystal structure

Heftetjernite crystallizes monoclinically in the space group P 2 / c (space group no. 13) with the lattice parameters a  = 4.784  Å , b  = 5.693 Å, c  = 5.120 Å and β = 91.15 ° and two formula units per unit cell . Template: room group / 13

The crystal structure of the mineral, which crystallizes in the wolframite structure type, is based on two types of distorted octahedra with common edges, which are mainly occupied by scandium and tantalum.

Heftetjernite is isotypic to the tungstates ferberite, hebnerite , sanmartinite, huanzalaite and the synthetic M 2+ WO 4 components with M = Mg, Co, Ni, Zn, and Cd. Synthetic components of the general formulas M 2+ MoO 4 ( M  = Mn, Co, Ni) and M 3+ NbO 4 ( M 3+  = Fe, In) as well as MnReO 4 and InTaO 4 are also isotypes .

properties

morphology

Heftetjernite occurs within voids in the albite on the surfaces of an X-ray amorphous Ti-Y-Ta-Nb mineral or included therein. It forms elongated tabular or columnar crystals up to 0.4 mm long and up to 0.1 mm wide, on which only the pinacoid {001} and either {010} or {001} have been identified. No twinning was observed.

physical and chemical properties

Stitched jernite crystals are deep dark brown and in some areas also greenish brown, their line color , on the other hand, is always dark brown with a reddish line.

The surfaces of the translucent to transparent crystals have a diamond-like sheen due to the very high refraction of light of n = 2.23 . In transmitted light, Heftetjernit shows normal interference colors and at most weak dispersion as well as a weak pleochroism from yellowish brown with a reddish tinge perpendicular to the longitudinal extension of the crystals to reddish brown parallel to it.

Heftetjernit has a very perfect cleavage according to {010}, but due to its brittleness breaks like amblygonite , whereby the fracture surfaces are uneven. In analogy to ferberite, a Mohs hardness of 4.5 is assumed for the mineral . Heftetjernite is one of the medium-hard minerals, stands between the reference minerals fluorite (hardness 4) and apatite (hardness 5) and, like these, can be easily scratched more (fluorite) or less (apatite) with a pocket knife. The calculated density for staple jernite is 6.44 g / cm³. Heftetjernit is neither in the long term nor in the short wavelength UV light , a fluorescent .

Education and Locations

Heftetjernite is a typical secondary mineral and arises from the oxidation of scandium-containing tantalum-niobium minerals. In the Heftetjern pegmatite, it formed in a cavity in the albite from an unidentified X-ray amorphous Ti-Y-Ta-Nb mineral. Further accompanying minerals are fluorite, muscovite , altered milarite and another unidentified metamictic , dark gray-brown mineral of the pyrochlore or microlith group. On two other samples, heftetjernite is accompanied by biotite , potassium feldspar and a metamictic mineral with a composition similar to Polykras- (Y) .

As a very rare mineral formation, Heftetjernite could so far (as of 2018) only be described by its type locality . The type locality is the scandium-rich Heftetjern pegmatite ( coordinates of the pegmatite Heftetjern ), a cleavelandite-amazonite pegmatite of the mixed LCT-NYF type (LCT =  lithium , cesium , tantalum - NYF = niobium, yttrium , fluorine ), which is located not far from the Town of Tørdal is located between Høydalen and Skarsfjell in the province ( Fylke ) Telemark, Norway. Locations for Heftetjernit in Germany , Austria and Switzerland are therefore unknown.

use

Heftetjernite would be an important scandium ore due to its high scandium content, but it is only of interest to mineral collectors due to its extreme rarity.

See also

literature

  • Uwe Kolitsch, Roy Kristiansen, Gunnar Raade, Ekkehart Tillmanns: Heftetjernite, a new scandium mineral from the Heftetjern pegmatite, Tørdal, Norway . In: European Journal of Mineralogy . tape 22 , no. 2 , 2010, p. 309-316 , doi : 10.1127 / 0935-1221 / 2010 / 0022-1987 .
  • Roy Kristiansen: A unique assemblage of Scandium-bearing minerals from the Heftetjern-pegmatite, Tørdal, south Norway (Kongsberg Mineralsymposium 2009) . In: Norsk Bergverksmuseum Skrift . tape 41 , 2009, p. 75-104 ( nags.net [PDF; 17.3 MB ; accessed on January 3, 2018]).
  • Heftetjernite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 311 kB ; accessed on January 3, 2018]).

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q Uwe Kolitsch, Roy Kristiansen, Gunnar Raade, Ekkehart Tillmanns: Heftetjernite, a new scandium mineral from the Heftetjern pegmatite, Tørdal, Norway . In: European Journal of Mineralogy . tape 22 , no. 2 , 2010, p. 309-316 , doi : 10.1127 / 0935-1221 / 2010 / 0022-1987 .
  2. ^ A b Roy Kristiansen: A unique assemblage of Scandium-bearing minerals from the Heftetjern-pegmatite, Tørdal, south Norway (Kongsberg Mineralsymposium 2009) . In: Norsk Bergverksmuseum Skrift . tape 41 , 2009, p. 75-104 ( nags.net [PDF; 17.3 MB ; accessed on January 3, 2018]).
  3. ^ Mindat - Heftetjern locality
  4. ↑ Steffen Jahn: New Minerals 1/2011 . In: Mineral World . tape 22 , no. 1 , 2011, p. 54-63 .
  5. ↑ Eligiusz Szełęg, Irina Gałuskina, Krystian Prusik: Sc – Nb oxide from corundum pegmatite of the Krucze Skały in Karpacz (Karkonosze massif, Lower Silesia, Poland) - a potentially new mineral of the ScNbO 4 - FeWO 4 series (20th General Meeting of the IMA (IMA2010), Budapest, Hungary, August 21-27) . In: CD of Abstracts . tape 6 , 2010, p. 501 ( rruff.info [PDF; 1,2 MB ; accessed on January 4, 2018]).
  6. ↑ Jakub Výravský, Radek Škoda, Milan Novak: Kristiansenite, thortveitite and SCNbO 4 : Products of Ca-metasomatism of Sc-enriched columbite- (Mn) from NYF pegmatite Kožichovice II, Czech Republic (PEG2017) . In: NGF Abstracts and Proceedings . tape 2 , 2017, ISBN 978-82-8347-019-2 , pp. 169-172 .
  7. ^ Roy Kristiansen: Heftetjernitt og triklin titanitt fra Heftetjern i Tørdal (in Norwegian) . In: stone . tape 37 , no. 4 , 2010, p. 20–22 ( nags.net [PDF; 445 kB ; accessed on January 5, 2018]).
  8. ↑ Mindat - Number of localities for Heftetjernit
  9. ↑ a b List of sites for Heftetjernit in the Mineralienatlas and Mindat
  10. ↑ Mindat - Heftetjernit