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An occurrence of tuite, γ‐Ca 3 ( PO 4 ) 2 , partly transformed from Ca‐phosphates in the Suizhou meteorite

2015; Wiley; Volume: 51; Issue: 1 Linguagem: Inglês

10.1111/maps.12577

1945-5100

Xiande Xie, Xiangping Gu, Ming Chen,

Planetary Science and Exploration

Abstract Tuite is a high‐pressure γ‐form of Ca 3 ( PO 4 ) 2 . An occurrence of tuite partly transformed from merrillite and chlorapatite was observed in the chondritic area adjacent to the shock veins in the Suizhou meteorite. Tuite grains are found in contact with both merrillite and chlorapatite, indicating two different transformation pathways. Tuite isochemically transformed from merrillite contains much higher contents of Na 2 O and MgO than those transformed from chlorapatite. Tuite transformed from merrillite does not contain Cl, but tuite transformed from chlorapatite contains 1.90–3.91 wt% of Cl, hence indicating an incomplete phase transformation from chlorapatite to tuite. P‐T conditions of above 12 GP a and 1100 °C are probably required for the transformation from merrillite and chlorapatite to tuite. A temperature gradient from the hot vein at 2000 °C to the surrounding chondritic area at 1000 °C corresponds to the partial phase transitions in the Suizhou phosphates. Fast cooling of the thin shock veins plays a key role in the preservation of phosphates that suffered partial high‐pressure phase transformation.