I doubt many is a old news, seen the found have
presented in the last Met.Society Meeting
A NEW IRON-NICKEL PHOSPHIDE FROM THE NORTHWEST AFRICA
1054 METEORITE. V. Moggi-Cecchi1, L.Bindi2, and G.
Pratesi2,3, 1Museo di Scienze Planetarie, Provincia di
Prato, Via Galcianese, 20/h, I-59100 Prato, Italy,
2Museo di Storia Naturale, Università degli Studi di
Firenze, I-50121 Firenze, Italy, 3Dipartimento di
Scienze della Terra, Università di Firenze, Via La
Pira, 4, I-50121, Florence, Italy
Introduction: NWA 1054 is a primitive achondrite
(acapulco-ite) with a main mass weighing 86 g. The
thin section displays a granular texture with olivine
and low-Ca pyroxene as major phases and high
Ca-pyroxene and plagioclase as minor; major
non-silicate phases are metal and troilite. Accessory
phases include merrillite, a Mg-rich chromite and two
iron-nickel phosphides. Terrestrial weathering grade
is low (W1) as well as shock stage (S1). The Museo di
Scienze Planetarie of Prato (MSP) owns the type
speci-men (MSP2366) [1].
Description: Six natural phophides are known:
schreibersite, (Fe,Ni,)3P, nickelphosphide (Ni,Fe)3P
[2], barringerite (Fe,Ni)2P [3], allabogdanite
(Fe,Ni)2P [4], florenskyite FeTiP [5] and perry-ite,
(Ni,Fe)8(Si,P)3 [6]. In the course of a study on some
acapulco-ites a new rather common iron-nickel
phosphide was discovered in the NWA 1052 and 1054
acapulcoites [7]. The chemical composi-tion of the new
phase, determined by EMPA, is
(Ni2.30Fe1.64Co0.01)Σ=3.95P1.05, pointing to a
4:1 metal/phosphorous ratio. It occurs as anhedral
grains up to 100 μm either associated with
kamacite (Fig. 1A) or with nickelphosphide (Fig. 1B).
Micro-indentation measurements provided a value (447
kg/mm2) lower than nickelphosphide. In reflected
light, the new phase is cream-yellowish, non
pleochroic, isotropic, and shows no bireflectance,
without internal reflections. Reflectance values are
60.56, 50.44 52.51 and 55.94 % at 471.1, 548.3, 586.6,
and 652.3 nm, respec-tively. A single-crystal X-ray
diffraction study, carried out on a small crystal
fragment, indicates a cubic lattice with a = 6.025 ±
0.001 and points to a space group P213 with Z = 4.
Both the coor-dination-number (12) and the density
(7.882 g/cc) are the highest ever reported for
phosphorus and iron-nickel phosphides, respec-tively.
Conclusions: The structure and the physical properties
suggest that the new iron nickel phosphide could play
an important role for Earth’s core mineralogy. Due to
the presence of this phase NWA 1054 acapulcoite seems
to be a really peculiar acapulcoite if com-pared with
literature data [8-9].
References: [1] Moggi Cecchi V. & Pratesi G. (2005)
MAPS, 40, in press [2] Skála R. & Drábek M. (2003)
Min. Mag. 67, 783 [3] Buseck P.R. (1969) Science
165,169 [4] Britvin S.N. et al., (2002) Am. Min.. 87,
1245 [5] Ivanov A.V. et al., (2000) Am. Min. 85, 1082
[6] Okada A. et al. (1988) MAPS 23, 59 [7]
Moggi-Cecchi V., Pratesi G., Mancini L., (2005) LPSC.
XXXVI, abs. #1808 [8] Patzer A., Hill D.H., Boynton
W.V. (2004) MAPS 39, 61 [9] Scott E.R.D. & Pinault,
L.J. (1999) LPSC. XXX, abs. #1507.
Matteo
--- Göran Axelsson <[EMAIL PROTECTED]> ha scritto:
What is the big news?
Merrillite (Ca3(PO4)2) is found in several
meteorites. From martian
meteorites () to pallasites (Springwater). Another
meteorites containing
merrillite are Portales Valley, Forest Vale,
Ankober, Allegan, Allegan,
Estacado, and several more.
And among the acapulcoites are Dhofar 1222.
It doesn't seem to be such a rare phosphate to me.
/Göran
M come Meteorite Meteorites wrote:
Hello
Today in the Museo di Scienze Planetarie of Prato
it
comes presented the new Iron-Nichel posphide found
in
my acapulcoite NWA 1054. The official name of the
posphide its melliniite.
Matteo
M come Meteorite - Matteo Chinellato
Via Triestina 126/A - 30030 - TESSERA, VENEZIA,
ITALY
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Via Triestina 126/A - 30030 - TESSERA, VENEZIA, ITALY
Email: [EMAIL PROTECTED]
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