Davisite

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Davisite
General and classification
other names

Scandium-Fassait, Sc-Fassait, IMA 2008-030

chemical formula CaScAlSiO 6
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DA.15
65.1.3.7
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group C 2 / c (No. 15)Template: room group / 15
Lattice parameters a  = synthetic: 9.884 (2)  Å ; b  = synthetic: 8.988 (1) Å; c  = synthetic: 5.446 (1) Å
α  = 90 °; β  = synthetic: 105.86 (1) °°; γ  = 90 °
Formula units Z  = 4
Physical Properties
Mohs hardness not determined
Density (g / cm 3 ) synthetic: 3.37 (calculated); natural: 3.38 (calculated)
Cleavage not determined
Break ; Tenacity not determined
colour colorless - gray
Line color not determined
transparency transparent
shine not determined
radioactivity -
magnetism -
Crystal optics
Refractive index n  = natural: 1.736 (calculated)
Birefringence δ = not determined
Optical character not determined
Axis angle 2V = not determined

The mineral Davisite is an extremely rare chain silicate from the pyroxene group with the idealized chemical composition CaScAlSiO 6 .

Davisite crystallizes with monoclinic symmetry and forms colorless crystals of a few µm in size.

Davisite has only been found in a few meteorites so far . It is one of the first minerals to crystallize out of the presolar nebula during the formation of the solar system and was found in calcium-aluminum-rich inclusions (CAI) of some meteorites. The type locality is the Allende meteorite , in which davisite occurs together with perovskite and spinel .

Etymology and history

The first scandium pyroxenes were synthesized and described in 1978 by Haruo Ohashi of the "National Institute for Researches in Inorganic Materials" (NIRIM) in Sakura (Chiba) , Japan .

The first description of a natural Sc-rich pyroxene was provided by Andrew M. Davis of the University of Chicago . In 1984 he described an unusual inclusion of scandium and zirconium- rich pyroxene, yttrium- rich perovskite , spinel and hibonite in the Ornans C3 chondrite .

Very few other scandium-rich pyroxenes were found in the following years, e.g. B. 1996 in the Murchison Meteorite , 2002 in CAI of the Efremovka Meteorite or 2003 in CAIs of the Ningqiang Carboniferous Chondrite .

25 years after the first description of a natural scandium pyroxene, Davisite was recognized as a separate mineral by the International Mineralogical Association (IMA) in 2009 . Chi Ma and George R. Rossman of the California Institute of Technology described Davisite from a CAI of the Allende meteorite and named the new mineral after Andrew M. Davis, the professor of cosmochemistry at the University of Chicago, who invented the first calcium-scandium pyroxene Ornans chondrites.

Davisite is one of only around 14 known scandium minerals and with jervisite the second from the pyroxene group .

classification

In the structural classification of the International Mineralogical Association (IMA) Davisit belongs together with pyroxene , Burnettit , diopside , Esseneit , Petedunnit , Grossmanit , Hedenbergit , Johannsenite , Kushiroit and Tissintit to Kalziumpyroxenen in pyroxene .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and has so far been used by the IMA, does not yet list the Davisite. It would have been assigned to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)". This section is further subdivided according to the type of chain formation, so that the mineral is classified according to its structure in the sub-section “Chain and band silicates with 2-periodic single chains Si2O6; Pyroxen-Familie "would be to be found, where together with Augite, Diopside, Esseneite, Petedunnit, Hedenbergit and Johannsenite to the" Ca-Klinopyroxene, Diopsidegruppe "with the system no. 9.DA.15 belonged to.

The obsolete, but still in use, 8th edition of the Strunz mineral classification system does not know the Davisite either. He would belong to the mineral class of "silicates and Germanates" and then "chain silicates and band silicates (inosilicates)" to the department of where he along with Aegirin , pyroxene, Petedunnit, Esseneit, Hedenbergit, jadeite , Jervisit , Johannsenite, kanoite , clino , Klinoferrosilit , Kosmochlor , Namansilit , Natalyit , Omphacit , Pigeonit and Spodumene the " Pyroxene group, subgroup Klinopyroxene" with the system no. VIII / F.01 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns davisite to the class of "silicates and Germanates" and there in the department of "chain silicate minerals". Here it is together with diopside, hedenbergite, augite, johannsenite, petedunnite and kushiroite in the group of " C 2 / c clinopyroxene (Ca-clinopyroxene)" with the system no. 65.01.03.7 can be found in the subsection " Chain Silicates: Simple unbranched chains, W = 1 with chains P = 2 ".

Chemism

Davisite with the idealized composition [M2] Ca [M1] Sc 3+ [T] (AlSi) O 6 is the scandium (Sc) analog of kushiroite ( [M2] Ca [M1] Al [T] (AlSi) O 6 ) and Esseneit ( [M2] Ca [M1] Fe 3+ [T] (AlSi) O 6 ), where [M2], [M1] and [T] are the positions in the pyroxene structure.

The compositions of the Davisite from the type locality is

  • [M2] Ca 0.989 [M1] (Sc 3+ 0.502 Mg 0.165 Ti 3+ 0.152 Ti 4+ 0.105 Zr 4+ 0.105 V 0.017 Y 0.012 Fe 2+ 0.010 Dy 0.003 Gd 0.002 Er 0.001 ) [T] (Si 1.028 Al 0.972 ) O 6 .

The magnesium contents go back to a mixed crystal formation with diopside,

  • [M1] Sc 3+ + [T] Al 3+ = [M1] Mg 2+ + [T] Si 4+ (diopside)

and the incorporation of titanium in Davisite takes place via two mixed crystal regions, corresponding to the exchange reactions

  • [M1] Sc 3+ = [M1] Ti 3+ ( Grossmanit )
  • [M1] Sc 3+ + [T] Si 4+ = [M1] Ti 4+ + [T] Al 3+ (Al-Buffonite)

In synthetic davisite the Al-Buffonite content is limited to ~ 34 mol% at 1 bar and 1420 ° C.

Davisite also forms mixed crystals with Zr-pyroxene, burnettite and kushiroite:

  • [M1] Sc 3+ + [T] Si 4+ = [M1] Zr 4+ + [T] Al 3+
  • [M1] Sc 3+ = [M1] V 3+ (burnettite)
  • [M1] Sc 3+ = [M1] Al 3+ (kushiroite),

where the kushiroite content does not exceed ~ 40 mol% at 1 bar and 1400 ° C.

Crystal structure

Davisite crystallizes with monoclinic symmetry in the space group C 2 / c (space group no. 15) with 4 formula units per unit cell . The lattice parameters of the synthetic end  link are a = 9.884 (2) Å, b  = 8.988 (1) Å, c  = 5.446 (1) Å and β = 105.86 (1) °. Structural investigations on natural davisite are also consistent with these values. Template: room group / 15

The structure is that of clinopyroxene. Silicon (Si 4+ ) and aluminum (Al 3+ ) occupy the tetrahedral T position surrounded by 4 oxygen ions, calcium (Ca 2+ ) occupies the octahedral M2 position surrounded by 6 oxygen and the octahedral M1 position is with Scandium (Sc 3+ ) occupied.

Education and Locations

Pure Davisite is stable over a wide temperature and pressure range. At 1 bar, Davisite melts incongruently with scandium oxide (Sc 2 O 3 ) and melt above 1530 ° C. At high pressures above 22 kbar , Davisite breaks down to eringaite , a scandium garnet and oxides.

Davisite has so far only been found in meteorites, where it occurs in calcium-aluminum-rich inclusions (CAI). The high concentration of rare elements with high melting points such as scandium, zircon and various rare earth metals allows two mechanisms for the formation of davisite. On the one hand, davisite may have deposited itself as one of the first compounds at very high temperatures when the presolar nebula cooled down. On the other hand, Davisite can be a residue from the heating and melting of CAIs, in which low melting point elements such as sodium, magnesium and silicon have evaporated. This would also lead to an accumulation of the high-melting elements in the remaining melt.

The type locality is the Allende meteorite , a carbonaceous chondrite that struck on February 8, 1969 near Parral in Chihuahua , Mexico . Davisite was discovered here in CAIs, where it occurs along with perovskite and spinel . Formation through premature condensation from the presolar nebula is assumed for this occurrence.

In the Ornans C3 chondrite, Davisite was found in the unusually scandium-rich CAI "OSCAR". OSCAR consists primarily of davisite with inclusions of perovskite, spinel, hibonite and molybdenum - osmium - and iridium - rich metal grains.

In Murchison CM2 chondrite Davisit in the CAI was found "HIB-11", where he also has inclusions of perovskite and spinel as well as numerous small cavities. The distribution pattern of the rare earths and titanium isotopes also suggests formation through premature condensation in the presolar nebula.

In the CAI 101.1 from the Efremovka meteorite, a carbonaceous chondrite of the type CV3, Davisite occurs as an encrustation of perovskite, together with spinel and gehlenite- rich melilite, in which there are inclusions of metallic NiFe. The history of these inclusions is complex, beginning with the early condensation of Sc, - Zr and rare earth-rich Ca-Al compounds, remelting and aggregation of various inclusions and subsequent oxidation . Davisite was formed after partial melting during the reaction of perovskite with an Sc-Zr-rich calcium aluminate melt.

In the CAI NQJ3–5–7 of the Coalite Chondrite Ningqiang, Davisite is found together with Hedenbergite as an inclusion in Gehlenite.

In the Vingarano CV3 meteorite, Davisite was found together with scandium-rich diopside, hexaferrum and spinel in amoeboid forsterite . Davisite here encloses inclusions of eringaite and tazheranite , from which it was formed in a reaction with spinel or the gas of the presolar nebula.


Web links

Individual evidence

  1. ^ Davisite in: IMA Database of Mineral Properties
  2. ↑ a b c d Davisit at mindat.org
  3. ↑ a b c d e f g Haruo Ohashi and Nobuo Ii: Structure of calcium scandium aluminum silicate (CaScAlSiO6) -pyroxene. In: Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists . tape 73 , 1978, pp. 267–273 ( rruff.info [PDF; 453 kB ; accessed on February 13, 2019]).
  4. ↑ a b c d e f g h i j k Chi Ma and George R. Rossman: Davisite, CaScAlSiO6, a new pyroxene from the Allende meteorite . In: American Mineralogist . tape 94 , 2009, p. 845–848 ( rruff.info [PDF; 407 kB ; accessed on February 13, 2019]).
  5. ↑ a b Haruo Ohashi: STUDIES ON CaScAlSiO6-PYROXENE . In: Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists . tape 73 , 1978, pp. 58–61 ( jst.go.jp [PDF; 198 kB ; accessed on February 15, 2019]).
  6. ↑ a b c Haruo Ohashi: SOLUBILITY OF CaAl2SiO6 IN CaScAlSiO6-PYROXENE . In: Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists . tape 73 , 1978, pp. 191–196 ( jst.go.jp [PDF; 337 kB ; accessed on February 15, 2019]).
  7. ↑ a b Haruo Ohashi and Masami Sekita: Raman spectroscopic study of clinopyroxenes in the join CaScAlSiO6-CaTiAl2O6 . In: Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists . tape 78 , 1983, pp. 239–245 ( jst.go.jp [PDF; 419 kB ; accessed on February 15, 2019]).
  8. ↑ a b AM Davis: A scandalously refractory inclusion in Ornans. In: Meteoritics . tape 19 , 1984, pp. 214 ( harvard.edu [PDF; 142 kB ; accessed on February 13, 2019]).
  9. ↑ a b STEVEN B. SIMON, ANDREW M. DAVIS AND LAWRENCE GROSSMAN: A unique ultrarefractory inclusion from the Murchison meteorite . In: Meteoritics & Planelay Science . tape 31 , 1996, pp. 106–115 ( wiley.com [PDF; 1,2 MB ; accessed on February 13, 2019]).
  10. ↑ a b A. EL GORESY, E. ZINNER, S. MATSUNAMI, H. PALME, B. SPETTEL, Y. LIN and M. NAZAROV: Efremovka 101.1: A CAI with ultrarefractory REE patterns and enormous enrichments of Sc, Zr, and Y in Fassaite and Perovskite . In: Geochimica et Cosmochimica Acta . tape 66 (8) , 2002, pp. 1459-1491 ( semanticscholar.org [PDF; 1.6 MB ; accessed on February 13, 2019]).
  11. ↑ a b Yangting LIN, Makoto KIMURA and Daode WANG: Fassaites in compact type A Ca-Al-rich inclusions in the Ningqiang carbonaceous chondrite: Evidence for partial melting in the nebula . In: Meteoritics & Planetary Science . tape 38 (3) , 2003, p. 407-417 ( wiley.com [PDF; 6.5 MB ; accessed on February 13, 2019]).
  12. ↑ Webmineral - Mineral Species Containing Scandium .
  13. ^ A b Chi Ma, John R. Beckett, and George R. Rossman: Grossmanite, Davisite, and Kushiroite: Three Newly-approved Diopside-Group Clinopyroxenes in CAIs . In: Lunar and Planetary Science Conference . tape 41 , 2010 ( usra.edu [PDF; 996 kB ; accessed on February 13, 2019]).
  14. ↑ Find location list for Davisite at the Mineralienatlas and at Mindat
  15. ↑ Chi Ma: DISCOVERY OF METEORITIC ERINGAITE, Ca3 (Sc, Y, Ti) 2Si3O12, THE FIRST SOLAR GARNET? In: 75th Annual Meteoritical Society Meeting (2012) . 2012 ( usra.edu [PDF; 70 kB ; accessed on September 9, 2017]).