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ITQIY meteorite, al-Saqiyah al-Hamra'a (Saguia el Hamra), Western Sahara

Enstatite
ITQIY meteorite, al-Saqiyah al-Hamra'a, Western Sahara

Photo: Thomas Witzke
Latitude: 26°35'27"N
Longitude: 12°57'8"W
Primitive Enstatite Achondrite [or Shock-melted Enstatite Chondrite]
1990 fall. 2 pieces, 410g and 4310g.

After a striking burst of light-and-sound, a 410 g stone was recovered by a nomad. A decade later a 4.31 kg stone was recovered — and the news of Itqiy spread. The dominant constituent of Itqiy is enstatite accompanied by kamacite (~ 25 vol%) and tiny kamacite-sulfide intergrowths. The very reduced mineralogy, the oxygen isotopes, and the cosmic ray exposure age all indicate that Itqiy is a member of the Enstatite-rich meteorite clan, initially described as an Enstatite chondrite, but beyond that classification is elusive. The enstatite resembles that of EL chondrites, but the metal is closer in composition to that of EH chondrites. Furthermore, Itqiy lacks chondrules and chondrule relics. This may be entirely due to impact melting from pre-terrestrial shock, but that is a hypothesis — not a conclusion. To begin with there is apparently no consensus on the level of shock.

The actual issues are deeper than that. Over two decades ago Klaus Keil (1989) argued that the Enstatite meteorites were derived from a minimum of four parent bodies (EH and EL chondrites, normal aubrites, and the Shallowater parent body). Recently, however, it has become increasingly difficult to accommodate several Enstatite meteorites into the four homeworld framework. Worlds which have been completely melted (e.g., Happy Canyon, Itqiy, NWA 2526) are especially difficult to understand. First, disentangling the effects of internally generated metamorphism from external shock(s) is difficult. Secondly, it is not clear whether all of the Enstatite-rich oddballs are derived from the four putative homeworlds. Recently, Keil and Bischoff (2008) have proposed that Itqiy and NWA 2526 may be derived from a fifth parent body.

Good Initial Reference:
Patzer, A., Hill, D. H. & Boynton, W. V. (2001) Itqiy: A metal-rich enstatite meteorite with achondritic texture, Meteoritics & Planetary Science 36 (11): 1495-1505. (Nov 2001).

Mineral List

Alabandite
Daubréelite
Enstatite
Iron
var: Kamacite

Niningerite
Oldhamite
Perryite ?
Schreibersite ?
Troilite


9 entries listed. 8 valid minerals.

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References

Keil, K. (1989). Enstatite meteorites and their parent bodies, Meteoritics 24 (4): 195-208. (Dec 1989)

Patzer, A. et al., (2001) Itqiy: II. a Short Story About Its Noble Gases and Oxygen Isotopes, Meteoritics & Planetary Science 36 (Supplement): p. A158. (Sept 2001)

Grossman, J. N. & Zipfel, J. (2001). The Meteoritical Bulletin, No. 85, 2001, Meteoritics & Planetary Science 36 (Supplement): A293-A322. (Sept 2001)

Patzer, A., Hill, D. H., & Boynton, W. V. (2001). Itqiy: A metal‐rich enstatite meteorite with achondritic texture. Meteoritics & Planetary Science, 36(11), 1495-1505.

Keil, K. & Adolf Bischoff, A. (2008) Northwest Africa 2526: A partial melt residue of enstatite chondrite parentage, Meteoritics & Planetary Science 43 (7): 1233-1240. (July 2008)

Niekerk, D., Keil, K. & Humayun, M. (2014) Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their relation to enstatite chondrites, primitive enstatite achondrites, and aubrites: Meteoritics & Planetary Science, Online Early. (Mar 2014)

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