On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions
On the application of the IMA-CNMNC dominant-valency rule to complex mineral compositions
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DOI：
10.1180/mgm.2019.55
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发表时间：
2019-10-01
影响因子：
2.7
通讯作者：
Mills, Stuart J.
中科院分区：
文献类型：
--
作者：
Bosi, Ferdinando;Hatert, Frederic;Mills, Stuart J.
矿物种类应该通过端元公式和使用IMA-CNMNC推荐的优势价规则来识别。然而，在文献中也使用了优势端元方法。这两种方法通常是收敛的，但对于一些中间组合物，可以观察到优势价规则和优势端元方法之间的显着差异。例如，对于石榴石超群矿物，端元方法是模糊的，因为端元比例强烈依赖于计算顺序。由于这个原因，IMA-CNMNC强烈建议使用优势价规则来命名矿物，因为它单独可以导致明确的矿物识别。虽然优势价规则的简单应用对于许多矿物成分的鉴定是成功的，但有时它会导致端元公式不平衡，这是由于在两个位点上发生偶联的杂价取代以及在单个位点上发生的杂价取代。在这些情况下，使用位点-总电荷方法来确定优势根电荷排列可能是有用的，并在其上应用优势成分规则。优势价规则和位置-总电荷法可以被认为是矿物识别中相互补充的两种方法。他们的关键是找到最合适的根荷和原子排列，与端元公式所决定的压倒条件相一致。这些程序已于2019年5月获得IMA-CNMNC的批准。
Mineral species should be identified by an end-member formula and by using the dominant-valency rule as recommended by the IMA-CNMNC. However, the dominant-end-member approach has also been used in the literature. These two approaches generally converge, but for some intermediate compositions, significant differences between the dominant-valency rule and the dominant end-member approach can be observed. As demonstrated for garnet-supergroup minerals, for example, the end-member approach is ambiguous, as end-member proportions strongly depend on the calculation sequence. For this reason, the IMA-CNMNC strongly recommends the use of the dominant-valency rule for mineral nomenclature, because it alone may lead to unambiguous mineral identification. Although the simple application of the dominant-valency rule is successful for the identification of many mineral compositions, sometimes it leads to unbalanced end-member formulae, due to the occurrence of a coupled heterovalent substitution at two sites along with a heterovalent substitution at a single site. In these cases, it may be useful to use the site-total-charge approach to identify the dominant root-charge arrangement on which to apply the dominant-constituent rule. The dominant-valency rule and the site-totalcharge approach may be considered two procedures complementary to each other for mineral identification. Their critical point is to find the most appropriate root-charge and atomic arrangements consistent with the overriding condition dictated by the end-member formula. These procedures were approved by the IMA-CNMNC in May 2019.