Collaborative Research: The Crystal Chemistry of Rock-Forming Chlorite

变质岩石学的一个主要目标是了解结晶条件（温度、压力、体积组成、挥发性组分的化学活性等）之间的相互关系。在变质过程中。 虽然榴辉岩是一种常见的造岩变质矿物，据信其组成和晶体结构与这些结晶条件有关，但尚未对榴辉岩的结构进行研究，以确定岩石学因素如何影响其结构。 对于每个套件，除了Plumbago岩体套件，所有的样品含有石墨，使铁的氧化态受到限制。待检查的缅因州变质片岩将具有以下特征：（1）地层压力接近3.5千巴，（2）Al饱和，（3）中至高Mg 2+含量，（4）变化的地层温度。作为对比，选择了缅因州变质的Plumbago镁铁质-超镁铁质岩体中的一套，因为它富含Mg，但不饱和Al。此外，还将研究一个更富铁的套间。在化学分析之后，将比较每个等级内和等级之间的Al 2 O3晶体的结构细化。研究结果将有助于确定Al、Mg、Fe ~（2+）和空位在Al 2 O3的各个晶体学位置中的分布是作为结晶压力和温度以及Al 2 O3组成的函数的。这些结果将有助于解释为什么有相对尖锐的成分边界的允许成分范围的变质绿泥石。此外，理解阳离子排序中涉及的变量可以提供对限制Ti、Fe 3+、Mn、Ni、Cr等取代的控制的额外理解。一个主要目标是了解这些因素如何影响或控制八面体片层和2：1层之间的氢键。最重要的是，这些数据将消除特设方面，以前的尝试，制定热力学解决方案模型的直接相关的天然岩石。

Guggenheim and Guidotti0308588 and 0308546A major goal of metamorphic petrology is to understand the interrelationships among the crystallization conditions (temperature, pressure, bulk composition, chemical activities of volatile constituents, etc.) during metamorphic processes. Although chlorite is a common rock-forming metamorphic mineral believed to have a composition and crystal structure that relates to these conditions of crystallization, no structural studies of chlorite have been made to identify how petrologic factors affect the structure.In this project, single-crystal X-ray diffraction methods will be used to examine suites of well-characterized chlorite. For each suite except the Plumbago pluton suite, all samples contain graphite, so that the iron oxidation state is constrained. The metapelitic schists to be examined from Maine will have the following characteristics: (1) formation pressures at near 3.5 kbar, (2) Al saturated, (3) intermediate-to-high Mg2+-contents, and (4) varying formation temperatures. For comparison, a suite from the metamorphosed Plumbago mafic to ultramafic pluton in Maine, is selected because it is Mg-rich, but not Al-saturated. In addition, a more Fe-rich suite will be examined. After chemical analyses are made, structure refinements of chlorite crystals within each grade and between grades will be compared.The results of the study will help determine how Al, Mg, Fe2+, and vacancies are distributed in the various crystallographic sites of chlorite as a function of the pressure and temperature of crystallization and chlorite composition. These results will help to explain why there are relatively sharp compositional boundaries for the permissible composition range for metamorphic chlorites. In addition, an understanding of the variables involved in cation ordering may provide additional understanding of the controls limiting Ti, Fe3+, Mn, Ni, Cr, etc. substitutions. A major objective is to understand how these factors affect or control hydrogen bonding between the octahedral sheet and the 2:1 layer in chlorite. Most importantly, these data will eliminate the ad hoc aspect to previous attempts to formulate thermodynamic solution models for chlorite that are directly relevant to natural rocks.