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Northwest Africa 7812 (NWA 7812) meteorite, Mauritaniai
Regional Level Types
Northwest Africa 7812 (NWA 7812) meteoriteMeteorite Fall Location
MauritaniaCountry

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Locality type:Meteorite Fall Location
Meteorite Class:Angrite meteorite
Meteoritical Society Class:Angrite
Metbull:View entry in Meteoritical Bulletin Database


Angrite, quenched
Find, 2013; 46.2 g, single stone

The Northwest Africa 7812 meteorite (NWA 7812) is a single, rounded, black, fine-grained stone purchased in Erfoud, Morocco. The stone is much more magnesian than most other angrites. Small strongly-zoned olivine phenocrysts (0.3-0.8 mm long) and fairly homogeneous clinopyroxene phenocrysts (up to 0.45 mm long) are set in a fine-grained groundmass. The groundmass is dominated by bladed and intergrown grains of kirschsteinite, anorthite (An100), Ca-rich clinopyroxene, and ulvöspinel. Minor troilite is also present. Inclusions of Cr-Al spinel and pentlandite are found within olivine. Vesicular features were noted in several instances. Secondary barite is present in the groundmass and in microfractures. Calcite was noted as well.

NWA 7812 is one of 15 recovered angrite meteorites (as of July 2015). Meteorites like Mg-rich NWA 7812 and the more recently recovered 2014 NWA 8535, a dunite, are gradually making it clear that the angrite geochemical group of meteorites have sampled a surprisingly diverse set of Ca-rich mafic and ultramafic environments. A K-Ar age of ~3 Ga for NWA 7812 may be due to an ancient degassing event (probable collision). A reported cosmic-ray exposure age (CRE) of ~20-22 Ma does not overlap with CRE ages determined for other angrites. The surprising range in CRE ages for the angrites (<1 Ma—>50Ma without major clusters) appears to provide a parallel physical analog to the still emerging petrographic and mineralogical complexity of this set of ancient stones.

NOTE: We follow Meier et al. (2013) in listing Mauritania as the original site of the meteorite's recovery. As the geographical coordinates are presently unknown to the meteoritical community, the location is formally designated simply as Northwest Africa at the Meteoritical Bulletin Database.

Select Mineral List Type

Standard Detailed Strunz Dana Chemical Elements

Mineral List


9 valid minerals.

Meteorite/Rock Types Recorded

Note: this is a very new system on mindat.org and data is currently VERY limited. Please bear with us while we work towards adding this information!

Select Rock List Type

Alphabetical List Tree Diagram

Detailed Mineral List:

Anorthite
Formula: Ca(Al2Si2O8)
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Augite
Formula: (CaxMgyFez)(Mgy1Fez1)Si2O6
Description: Clinopyroxene phenocrysts w. alumina 16-18 wt.%.
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Augite var: Fassaite
Formula: (Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Description: Clinopyroxene phenocrysts w. alumina 16-18 wt.%.
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Baryte
Formula: BaSO4
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258
Calcite
Formula: CaCO3
Description: In microfractures within olivine xenocryst.
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258
'Fayalite-Forsterite Series'
Description: Olivine - Fa 8.8-46.0 mol% in MetBill#102. Olivine phenocrysts exhibit skeletal growth w. incomplete closure of crystal domains.
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Kirschsteinite
Formula: CaFe2+SiO4
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258
Pentlandite
Formula: (FexNiy)Σ9S8
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Spinel
Formula: MgAl2O4
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258; Irving, A. J., Kuehner, S. M., Chen, G., Conrey, R. M., Ziegler, K. & Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Troilite
Formula: FeS
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258
Ulvöspinel
Formula: TiFe2O4
Reference: http:www.lpi.usra.edu/meteor/metbull.php?code=57258

List of minerals arranged by Strunz 10th Edition classification

Group 2 - Sulphides and Sulfosalts
Pentlandite2.BB.15(FexNiy)Σ9S8
Troilite2.CC.10FeS
Group 4 - Oxides and Hydroxides
Spinel4.BB.05MgAl2O4
Ulvöspinel4.BB.05TiFe2O4
Group 5 - Nitrates and Carbonates
Calcite5.AB.05CaCO3
Group 7 - Sulphates, Chromates, Molybdates and Tungstates
Baryte7.AD.35BaSO4
Group 9 - Silicates
Anorthite9.FA.35Ca(Al2Si2O8)
Augite9.DA.15(CaxMgyFez)(Mgy1Fez1)Si2O6
var: Fassaite9.DA.15(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Kirschsteinite9.AC.05CaFe2+SiO4
Unclassified Minerals, Rocks, etc.
'Fayalite-Forsterite Series'-

List of minerals arranged by Dana 8th Edition classification

Group 2 - SULFIDES
AmBnXp, with (m+n):p = 9:8
Pentlandite2.7.1.1(FexNiy)Σ9S8
AmXp, with m:p = 1:1
Troilite2.8.9.1FeS
Group 7 - MULTIPLE OXIDES
AB2X4
Spinel7.2.1.1MgAl2O4
Ulvöspinel7.2.5.2TiFe2O4
Group 14 - ANHYDROUS NORMAL CARBONATES
A(XO3)
Calcite14.1.1.1CaCO3
Group 28 - ANHYDROUS ACID AND NORMAL SULFATES
AXO4
Baryte28.3.1.1BaSO4
Group 51 - NESOSILICATES Insular SiO4 Groups Only
Insular SiO4 Groups Only with all cations in octahedral [6] coordination
Kirschsteinite51.3.2.2CaFe2+SiO4
Group 65 - INOSILICATES Single-Width,Unbranched Chains,(W=1)
Single-Width Unbranched Chains, W=1 with chains P=2
Augite65.1.3a.3(CaxMgyFez)(Mgy1Fez1)Si2O6
Unclassified Minerals, Mixtures, etc.
Anorthite-Ca(Al2Si2O8)
Augite
var: Fassaite
-(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
'Fayalite-Forsterite Series'-

List of minerals for each chemical element

CCarbon
C CalciteCaCO3
OOxygen
O AnorthiteCa(Al2Si2O8)
O BaryteBaSO4
O CalciteCaCO3
O Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
O SpinelMgAl2O4
O UlvöspinelTiFe2O4
O KirschsteiniteCaFe2+SiO4
O Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
NaSodium
Na Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
MgMagnesium
Mg Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Mg SpinelMgAl2O4
Mg Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
AlAluminium
Al AnorthiteCa(Al2Si2O8)
Al Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Al SpinelMgAl2O4
SiSilicon
Si AnorthiteCa(Al2Si2O8)
Si Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Si KirschsteiniteCaFe2+SiO4
Si Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
SSulfur
S BaryteBaSO4
S Pentlandite(FexNiy)Σ9S8
S TroiliteFeS
CaCalcium
Ca AnorthiteCa(Al2Si2O8)
Ca CalciteCaCO3
Ca Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Ca KirschsteiniteCaFe2+SiO4
Ca Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
TiTitanium
Ti Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Ti UlvöspinelTiFe2O4
FeIron
Fe Augite (var: Fassaite)(Ca,Na)(Mg,Fe2+,Al,Fe3+,Ti)[(Si,Al)2O6]
Fe Pentlandite(FexNiy)Σ9S8
Fe TroiliteFeS
Fe UlvöspinelTiFe2O4
Fe KirschsteiniteCaFe2+SiO4
Fe Augite(CaxMgyFez)(Mgy1Fez1)Si2O6
NiNickel
Ni Pentlandite(FexNiy)Σ9S8
BaBarium
Ba BaryteBaSO4

References

Sort by

Year (asc) Year (desc) Author (A-Z) Author (Z-A)
Irving, A.J., Kuehner, S.M., Chen, G., Conrey, R.M., Ziegler, K., and Pitt, D. (2013) Petrologic, Elemental and Oxygen Isotopic Characterization of Mg-Rich, Olivine-Phyric Quenched Angrite Northwest Africa 7812: 76th Annual Meeting of the Meteoritical Society. Published in Meteoritics and Planetary Science Supplement 48, id.5249. (Sept 2013).
Meier, M.M.M., Irving, A.J., and Wieler, R. (2013) Cosmic-Ray Exposure and Gas-Retention Ages of the Unique Quenched Angrite Northwest Africa 7812: Published in Meteoritics and Planetary Science Supplement, id.5222. (Sept 2013).
Grady, M.M., Pratesi, G., and Moggi-Cecchi, V. (2015) Atlas of Meteorites. Cambridge University Press: Cambridge, United Kingdom. 373 pp.

External Links

http://www.lpi.usra.edu/meteor/metbull.php -Meteoritical Bulletin Database
http:www.lpi.usra.edu/meteor/metbull.php?code=xxxxx -NWA7812@MetBullDatabase
http://www.hou.usra.edu/meetings/metsoc2013/pdf/5249.pdf - Irving et al. (2013)


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