Merrillite, ideally Ca18Na2Mg2(PO4)14 (Dana No: 38.03.04.04; Strunz No: 08.AC.45), an analog to synthetic tricalcium phosphate β-Ca3(PO4)2, was identified as an inclusion in lower-mantle diamonds from the Rio Soriso area, Brazil. It was associated with former bridgmanite, CaSi- and CaTi-perovskites, and ferropericlase. This is the first report of merrillite in a terrestrial environment; previously, it was known only in meteorites and lunar rocks. The compositions of merrillite vary in different localities; the Rio Soriso sample was enriched in SO3 (2.03 wt%). Merrillite from lower-mantle diamonds may be a retrograde phase of the tuite [γ-Ca3(PO4)2]. Owing to their crystal structures, both merrillite and tuite may be important potential hosts for rare earth elements (REE) and large ion lithophile elements (LILE), including Sr and Ba, in the deep Earth. The find of merrillite suggests a larger variety of mineral species in the lower mantle than previously assumed.

中文翻译：

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首次在陆地环境中发现作为下地幔金刚石中的包裹体的钙镁石 Ca3(PO4)2

Merrillite，理想情况下是 Ca18Na2Mg2(PO4)14（Dana 编号：38.03.04.04；Strunz 编号：08.AC.45），是合成磷酸三钙 β-Ca3(PO4)2 的类似物，被确定为下地幔钻石中的内含物来自巴西里奥索里索地区。它与以前的布里奇曼石、CaSi 和 CaTi 钙钛矿以及方镁石有关。这是在陆地环境中首次报道红斑岩；以前，它只在陨石和月球岩石中被发现。不同地区的硅藻土成分不同；Rio Soriso 样品富含 SO3 (2.03 wt%)。来自下地幔钻石的 Merrillite 可能是 tuite [γ-Ca3(PO4)2] 的逆行相。由于它们的晶体结构，磷灰石和 tuite 都可能是稀土元素 (REE) 和大离子亲石元素 (LILE) 的重要潜在宿主，包括 Sr 和 Ba，在地球深处。merrillite 的发现表明下地幔中的矿物种类比以前假设的要多。