Natural sodium phlogopite coexisting with potassium phlogopite and sodian aluminian talc in a metamorphic evaporite sequence from Derrag, Tell Atlas, Algeria
Natural sodium phlogopite coexisting with potassium phlogopite and sodian aluminian talc in a metamorphic evaporite sequence from Derrag, Tell Atlas, Algeria
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天然钠金云母与钾金云母和钠铝滑石共存于阿尔及利亚德尔阿特拉斯 Derrag 的变质蒸发岩序列中
DOI：
10.1007/bf00371692
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发表时间：
1980
影响因子：
3.5
通讯作者：
H. Kulke
中科院分区：
文献类型：
--
作者：
W. Schreyer;K. Abraham;H. Kulke
目前已知的唯一自然产出的金云石是在白云石中发现的，白云石中含有钠长石、其他三种镁层状硅酸盐、电气石、石英、金红石和黄铁矿的大斑岩。钠金云母接近于理想式NaMg3[AlSi3O10](OH)2，尽管它们可能含有额外的Li。它们总是被钾金云母的薄层包覆，其八面体和四面体的占有率与钠金云母不同。这些边缘可能阻止了金云母的逆行水化，这似乎是天然岩石中普遍缺乏金云母的主要原因。对于白云石所经历的低级变质条件，钠和钾金云母之间存在溶液关系。至少在K金云母出现之前，钠金云母也存在，含有Na和Al[4]的滑石相取代了Si。这种从纯滑石到金云母的取代被发现延伸了36%。然而，这一相是真正的固溶体，还是滑石和金云母之间的无序混合层，目前还不能确定。最终出现在毫米级斑岩中的层状硅酸盐是斜长石和钠铝质滑石之间的1：1有序混合层，代表了一种新的矿物。据估计，在低水和二氧化碳逸度下的变质温度低于400°C。
In its only natural occurrence known thus far sodium phlogopite is found in a dolomite containing large porphyroblasts of albite, three other magnesium phyllosilicates, dravite-uvite tourmaline, quartz, rutile, and pyrite. Sodium phlogopites are close to the ideal formula NaMg3[AlSi3O10](OH)2, although they may possibly contain additional Li. They are invariably coated by thin rims of potassium phlogopite with octahedral and tetrahedral occupancies different from those of sodium phlogopite. These rims may have prevented the retrograde hydration of sodium phlogopite which seems to be the main reason for its general absence in natural rocks. For the low-grade metamorphic conditions undergone by the dolomite a solvus relationship is indicated between sodium and potassium phlogopite.Sodium phlogopite also coexists, at least prior to the appearance of K phlogopite, with a talc phase containing Na and Al[4] substituting for Si. This type of substitution leading from pure talc to sodium phlogopite was found to extend as far as 36 mole percent. However, the nature of this phase as a genuine solid solution or as a disordered mixed-layer between talc and sodium phlogopite could not be identified as yet. The final phyllosilicate appearing in millimeter-size porphyroblasts is an ordered 1∶1 mixed layer between clinochlore and sodian aluminian talc representing a new mineral.Metamorphic temperatures at the supposedly low water and CO2 fugacities are estimated to have been below 400 °C.