内蒙古霍各乞矿区含矿富石榴石岩晶体定量化结构分析及其意义

晶体粒度分布（CSD）是定量化分析火成岩和变质岩结构的重要手段。在变质岩中测量的CSD提供了有关变质过程中晶体成核和生长速率、生长时间的定量信息。文章选取内蒙古霍各乞二号矿床含矿富石榴石岩样品中石榴子石晶体为研究对象，在GIS软件和R语言的支持下，应用空间点模式分析、CSD分析、空间最邻近分析、空间多距离分析、Fry分析等综合方法，探讨了晶体空间数据和点空间数据表征的微结构变化特征，将CSD曲线分段变化记录的信息与地质演化历史联系起来。分段的CSD曲线记录了变质事件的叠加。不同形式的晶体粒度分布直接反映了区域变质岩与接触变质岩演化历史的差异。由于接触变质作用的高温阶段持续时间较短，因此产生的CSD曲线是线性的，不受退火的影响。而区域变质作用涉及长时间升温及其之后的冷却阶段，所以最初的线性CSD后来被退火改造为钟形曲线。含矿富石榴石岩样品的核密度和CSD分析结果显示了两个晶体群密度。分析认为一类晶体群可能与造山过程中的区域变质活动有关，另一类晶体群可能与大面积区域变质期后发生在特定位置的岩体侵入迅速升温的接触热变质事件有关。      

火成岩的晶体群与成因矿物学展望

岩浆系统物理过程的研究进展导致了岩浆系统成熟度的概念,因而认识到火成岩中的晶体并非全部由寄主熔体晶出。本文将火成岩中的矿物晶体按其加入岩浆系统的方式划分为3种晶体群:固体晶体群、熔体晶体群和流体晶体群。固体晶体群系指呈固态加入岩浆的晶体群,包括残留晶亚群和捕虏晶亚群;熔体晶体群系指从熔体中晶出的晶体群,包括从不同深度水平岩浆房中晶出的晶体亚群(岩浆房晶体亚群)、岩浆上升途中晶出的晶体亚群(通道晶体亚群)、在岩浆系统中长期循环的晶体亚群(循环晶亚群)和岩浆侵位后晶出的晶体亚群(基质晶亚群)。流体晶体群系指从流体相晶出的晶体群,包括从超临界流体晶出的晶体亚群(超临界晶体亚群)、从气体晶出的晶体亚群(凝聚晶体亚群)和从热液晶出的晶体亚群(热液晶体亚群)。这种划分方案为火成岩成因矿物学研究打开了新的窗口,阐明不同晶体群的标型特征和形成条件是成因矿物学研究的重要任务。理论上,残留晶与原生岩浆保持热力学平衡,捕虏晶一般与岩浆不平衡,熔体晶体群在岩浆系统演化的特定阶段上与岩浆保持热力学平衡,而流体晶体群则一般不与岩浆平衡,但超临界晶体亚群可部分与岩浆平衡。各种晶体群在火成岩中的保存程度与岩浆系统的存续时间尺度和晶体吸收速率紧密相关。在快速上升和固结的岩浆系统中,所有的晶体群都有可能得到保存。相反,在缓慢上升和固结的岩浆系统中,有可能仅保留有基质晶亚群。因此,晶体群的数量和颗粒大小可以用来定性评价岩浆系统存活的时间尺度,定量化结构分析将成为成因矿物学的重要研究内容。     

运用定量化结构分析方法揭示蚀变花岗斑岩的形成过程——以新疆莫阿特茂金岩体为例

地球化学分析方法已广泛运用于火成岩成因的研究中,但对于一些蚀变较严重的岩石,有时仅通过地球化学分析难以还原岩浆固结的过程。火成岩定量化结构分析方法是通过对岩石中矿物的定量分析(诸如晶体粒度分布分析,晶体空间分布分析,以及晶体定向程度分析等),从而反演岩浆固结过程中发生的动力学过程。这种方法很好地避免了蚀变作用对还原岩体形成过程所产生的诸多影响。本文运用火成岩定量化结构分析方法,对新疆莫阿特茂金花岗斑岩体钻孔中10个样品的钾长石斑晶和石英斑晶分别进行分析。尽管这些样品普遍发生了碳酸盐化蚀变作用,定性观察中结构特征也比较均一,但是钾长石和石英斑晶的定量化结构数据及其在钻孔深度(约170 m)范围内的变化趋势显示,茂金花岗斑岩体可能至少由4次脉冲岩浆叠加形成,每股岩浆中心的CSD曲线小晶体缺乏,发生了粗化现象。由于脉冲式岩浆多次注入,导致的温度振荡加剧了矿物粗化。脉冲岩浆中心处斑晶体积含量的增加,可能与岩浆流动过程中对大晶体的影响有关,80 m深度以下脉冲岩浆接触带的斑晶体积含量明显增加,是由于机械压缩导致的。     

定量化火成岩结构分析与岩浆固结的动力学过程

定量化火成岩结构分析将传统的定性或半定量化的岩相学研究提高到了与岩石地球化学分析相比拟的定量化程度,实现了诸如晶体粒度分布、晶体空间分布、晶体定向程度分析和二面角测量等方面的定量化研究。集中介绍了以上4种国际上应用广泛的定量化火成岩结构分析方法,包括各种研究方法的基本理论公式、岩浆动力学意义和实现方式。详细介绍了定量化火成岩结构分析中处于核心地位的晶体粒度分布理论,概括了二维岩石薄片法、三维连续剖面法和X射线层析技术,在定量化火成岩结构分析中的应用原理和现状。对晶体粒度分布分析中数据的封闭性和有效性检验进行了简要论述。综合阐述了晶体成核生长,晶体的聚集、分离和分解,岩浆混合,压滤、压熔和岩浆流动,结构的调整和平衡等一些基本的岩浆动力学过程中晶体粒度分布特征的表现。结合一些已发表的晶体粒度分布和晶体空间分布数据,简要概括了重要的基本定量化火成岩结构参数所表达的封闭和开放岩浆体系的特征,以及参数间协变关系所反映的岩浆固结动力学过程。最后给出了二维岩石光薄片分析法的基本流程和注意事项,认为今后定量化火成岩结构分析和地球化学分析结合在一起的综合方法,将成为研究成岩成矿动力学过程的重要手段,也将会逐步扩展到岩浆相关矿床中成岩成矿机制分析和成矿预测的方向。     

攀枝花铁矿朱家包包矿段层状铁矿体的成因:来自矿物结构定量化分析的证据

岩浆型铁矿床是中国最重要的铁矿类型之一,攀枝花式铁矿赋存于攀枝花大型层状侵入体中,同时是峨眉山地幔柱系统的组成部分。然而此类矿床的成因问题仍未得到有效的解决。文中以攀枝花铁矿朱家包包矿段中部岩相带(MZ)为例,采用定量化结构分析的方法,结合地质学和岩相学观察结果,试图从攀枝花岩体中部岩相带辉长岩中单斜辉石的结构角度解释攀枝花式铁矿层状矿体的成因。岩相学观察可见部分样品中单斜辉石和斜长石具有明显的溶蚀结构以及角闪石、蛇纹石的增生边,被溶蚀的部分由铁钛氧化物填充,而铁钛氧化物之间发育共结结构。晶体粒度分布(CSD)显示,被溶蚀的单斜辉石较未溶蚀样品具有更陡的CSD曲线斜率,CSD曲线小颗粒处弯曲程度更大,以及更高的铁矿含量,说明溶蚀作用导致了CSD曲线变得更陡,产生了类似于粗化作用的CSD曲线。晶体空间分布(SDP)显示中部岩相带岩体上部有分选的趋势,而岩体下部则表现出挤压的趋势,说明了岩体上部保留了岩浆结晶过程中的矿物颗粒分选的趋势,而下部由于普遍的溶蚀导致了矿物粒间空隙增大,难以支撑上部的荷载,表现出挤压趋势。造岩矿物溶蚀、富水的角闪石、蛇纹石生长边以及填隙的铁钛氧化物说明有流体存在。在攀枝花岩体中段结晶晚期,富铁流体加入半固结的岩体使得造岩矿物溶蚀,而后填充于空隙,流体逃逸后铁矿物富集沉淀成矿。岩体下部具普遍的溶蚀作用,受荷载富铁流体被挤压逃逸,形成了块状的贫铁岩体;上部流体水平运移,没有受到挤压作用,流体逃逸后保留了铁矿的含量,形成了富集的层状铁矿体。这种层状矿体的成因模型类似于透岩浆流体模型。     

东昆仑造山带家琪式斑岩型Cu-Mo矿床中花岗闪长岩的斜长石晶体群及其成矿意义

近年来,越来越多的作者接受火成岩由多种晶体群组成的新概念。本文以东昆仑造山带家琪式斑岩型Cu-Mo矿床中花岗闪长岩为例,试图阐明火成岩晶体群的涵义及其研究方法和意义。显微镜观察表明,花岗闪长岩的斜长石按其结晶习性可划分为5种不同类型,阴极发光图像分析证实了这一观察,并揭示了它们的生长过程。电子探针剖面分析揭示了横跨晶体切面的化学变化,进一步表明这些晶体具有不同的生长环境和生长过程,属于不同的晶体群。基于平衡热力学原理,推测晶体群来自5个不同的岩浆子系统,暗示形成花岗闪长岩的岩浆为多重岩浆房系统岩浆混合作用的产物,且混合岩浆经历了快速固结过程。这些认识对于探讨斑岩型矿床成因具有重要意义。     

岩石的晶体粒度分布(CSD)和结晶作用的动力学与力学(Ⅰ.理论)

结晶岩的晶体粒度是生长速率与年龄的主要量度。而当成核作用在短时期内产生大量晶体时,则有可能在结晶作用过程中出现大范围的晶体粒度。以各种粒度的晶体数量密度为根据的布居平衡,一般预示随粒度增大的对数线性分布。这样分布的负斜率是衡量整个布居生长速率与平均年龄乘积的尺度而零粒度截距为成核密度。当这样绘图而且能用Randolph和Larson(1971)在化学工程方面建立的CSD理论加以解释时,对许多熔岩观察到的晶体粒度分布(CSD)如果不是线性的也是圆滑而有规律的。根据这样的数据可以估算出成核密度,成核速率与生长速率和动力学反应的等级而且通过解析模型则能精确计量影响CSD的物理作用过程(例如,晶体分离作用和晶体堆积作用,布居的混合,变质岩和深成岩中的退火作用以及晶核的破坏)。CSD理论对影响结晶作用的动力学和物理作用过程的宏观研究提供一种形式,能分析并检验化学和物理作用过程对CSD的明显影响。这是一种能把岩相学资料与结晶作用动力学定量地联系起来的方法,而且在这些基础上CSD对实验室研究提供主要的补充资料,在这三部分连载的文章中,第1部分提供在地质学范围内的一般CSD理论,在第1和第1部分中分别提出对火成岩及变质岩的应用。     

四川米易青皮村镁铁质侵入体的固结过程

含矿与无矿侵入体的区分是阐明岩浆型矿床成因的基础,也是深部找矿预测的依据。本文选择四川米易青皮村岩体为例,通过岩相学及矿物成分剖面和定量化结构分析,试图阐明无矿岩浆侵入体的固结过程,并与攀枝花含矿岩体对比,进一步揭示含矿与无矿侵入体形成过程的区别。岩相学分析表明,青皮村岩体中粒辉长岩的造岩矿物可以划分为四个世代：①粗粒斜长石→②中粒斜长石+单斜辉石→③黑云母+铁钛氧化物→④伟晶状斜长石,展示了封闭系统的固结过程。加上粗晶辉长岩脉的矿物组合钠长石+单斜辉石+角闪石+磷灰石,可以将青皮村岩体的组成矿物划分为5个世代,进而划分成四个晶体群：通道晶体群、岩浆房晶体群、基质晶体群和流体晶体群。晶体成分剖面分析表明,通道晶和岩浆房晶显示正环带,具有封闭系统降温结晶的特点,其中通道晶的生长伴随着减压作用;基质晶初始为正环带,末期显示反环带,反映了残余流体的聚集与逃逸;而流体晶体群的产出则反映了超临界流体的相分离和排气作用。定量化结构分析揭示了岩浆固结晚期的粗化过程,是封闭岩浆系统固结过程的重要证据,与岩相学和晶体成分剖面分析结果一致。此外,青皮村岩体中Fe Ti氧化物含量甚低,其体积分数仅为4%,暗示它们不可能聚集成矿。与攀枝花岩体相比,青皮村岩体固结过程中缺失先存晶体的溶蚀结构,后者被认为是高温含矿流体输入的结果。据此,本文提出,外来含矿流体(透岩浆流体)输入与否决定了镁铁质岩浆侵入体的产矿能力;进而认为,是流体输入导致了岩浆分异,而不是岩浆分异产生了含矿流体。     

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新书要览定量晶体光学及其应用朱中一，地质出版社，１９９３，１６ｋ，７４ｐ详细介绍了单偏光下定量晶体光学特征及矿物百分含量统计和粒度分析应用，阐述了正交偏光下的定量晶体光学特征和光学岩组测量与折射率测量原理，还介绍了锥光和非正交偏光下定量晶体光学及其应...     

土壤剖面的磁学特征及其对交通污染的指示意义——以北京首都机场高速公路为例

对北京首都机场高速公路旁采集的土壤柱状T01剖面的磁学参数和金属元素分析,探讨了研究区内现代交通导致的土壤磁学性质的变化及其对环境污染的响应.结果表明,磁参数(χ,ARM和SIRM)与重金属含量呈同步垂向变化趋势.来源于交通运输排放的污染物是土壤剖面上部(0～8 cm)磁性和金属含量增强的主要原因,8cm以下,土壤基本未受到污染,磁性矿物和重金属含量较低,磁性颗粒变化稳定,基本代表了该地区土壤的自然背景.尽管土壤岩石磁学分析表明剖面上下部受污染和未受污染样品的磁载体均是粒度较粗的多畴磁铁矿,但是结合磁参数比值曲线,说明底部样品的磁颗粒的粒度较顶部偏细.磁性矿物的含量变化没有影响磁颗粒的粒度特征.指标聚类等相关分析表明,土壤磁参数(χ,ARM和SIRM)与重金属元素(Pb,Zn和Cu)含量显著相关;结合模糊聚类分析,磁参数可用于追踪、识别交通污染物质在土壤剖面中的富集、迁移状态,揭示不同深度土壤的污染程度.     

Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization

Crystal-size in crystalline rocks is a fundamental measure of growth rate and age. And if nucleation spawns crystals over a span of time, a broad range of crystal sizes is possible during crystallization. A population balance based on the number density of crystals of each size generally predicts a log-linear distribution with increasing size. The negative slope of such a distribution is a measure of the product of overall population growth rate and mean age and the zero size intercept is nucleation density. Crystal size distributions (CSDs) observed for many lavas are smooth and regular, if not actually linear, when so plotted and can be interpreted using the theory of CSDs developed in chemical engineering by Randolph and Larson (1971). Nucleation density, nucleation and growth rates, and orders of kinetic reactions can be estimated from such data, and physical processes affecting the CSD (e.g. crystal fractionation and accumulation, mixing of populations, annealing in metamorphic and plutonic rocks, and nuclei destruction) can be gauged through analytical modeling. CSD theory provides a formalism for the macroscopic study of kinetic and physical processes affecting crystallization, within which the explicit affect of chemical and physical processes on the CSD can be analytically tested. It is a means by which petrographic information can be quantitatively linked to the kinetics of crystallization, and on these grounds CSDs furnish essential information supplemental to laboratory kinetic studies. In this three part series of papers, Part I provides the general CSD theory in a geological context, while applications to igneous and metamorphic rocks are given, respectively, in Parts II and III.     

Crystal Size Distribution (CSD) and Textural Evolution of Accessory Apatite, Titanite and Allanite during Four Stages of Metamorphism: an Example from the Moine Supergroup, Scotland

Crystal size distributions (CSD) and shapes of accessory apatite,titanite and allanite are investigated in three texturally distinctgarnet zones (Z1–Z3) and in the matrix (Z4) of a garnet–epidote–biotitegneiss from the Moine Supergroup. Additionally, textural relationshipsand interactions between the accessory minerals and surroundingrock-forming minerals are considered, results of numerical CSDmodelling are presented, and geochronological and geologicalconsequences of the inferred CSD evolutions are discussed. Texturesand CSDs indicate that the accessory minerals were in, or near,a stage of nucleation and initial growth immediately prior togarnet Z1 overgrowth, and formed within less than 20 000 years,either by a size-independent or size-dependent growth mechanism.Subsequently, the CSDs were modified by different growth mechanisms,as supported by several parameters including CSDs, grain numbers,grain sizes, specific volumes and others. The apatite CSD evolutionfrom Z1 to Z4 is consistent with open-system LPE (Law of ProportionateEffects) growth accompanied and followed by supply controlledrandom ripening, whereas transformation of the original titaniteCSD is more consistent with Ostwald ripening, temporarily accompaniedby positive or negative McCabe growth. The allanite CSDs alsopoint to Ostwald ripening between Z3 and Z4. The textural observationsindicate that the growth evolution of the accessory phases wasinfluenced by mineral reactions with surrounding rock-formingminerals, as well as by deformation and matrix coarsening, ina manner similar to that found in more simple ceramic systems.The observed textures require a successive temperature risethroughout the tectono-metamorphic evolution of the investigatedrock, in agreement with existing P–T data. Fast nucleationand initial growth of the accessory minerals during Z1 was perhapsinitiated by contact metamorphism, whereas subsequent growthand annealing (Z2–Z4) result from regional metamorphicevents. KEY WORDS: apatite; titanite; allanite; CSD; Moine Supergroup; textures; kinetics     

准噶尔盆地老山沟火山岩晶体粒度分布及其结晶动力学意义

摘　 要　 阐述了火山岩晶体粒度分布的基本原理和研究方法‚分析了老山沟火山岩斜长石、 辉石、橄榄石、铁钛氧化物的晶体粒度分布。前3种矿物在中间粒度处发生了有意义的弯折‚ 原因是岩浆上升时过冷度增大。估算了岩浆房中斜长石、橄榄石的成核速率、结晶时间及上 升过程中处于结晶带的时间。研究表明‚在岩浆的演化过程中‚晶体的分离和累积作用及岩 浆的混合和对围岩的同化作用可以忽略。     

Quantifying the Building Blocks of Igneous Rocks: Are Clustered Crystal Frameworks the Foundation?

Most phenocryst populations in volcanic rocks, and those preservedin shallow-level igneous intrusions, are clustered (variouslyreferred to as clots, clumps or glomerocrysts). These clustersof crystals are the building blocks that accumulate to formthe high-porosity, touching crystal frameworks from which igneouscumulates form. Examination of touching crystal frameworks inolivine- (komatiite cumulates and experimental charges) andplagioclase-dominant crystal populations (Holyoke flood basalt,Connecticut, USA) reveal complex, high-porosity, clustered crystalarrangements. Olivine touching frameworks in komatiite flowsare interpreted to form in hundreds of days. Plagioclase frameworksare calculated to have formed in less than 17 years for a crystalgrowth rate of 1 x 10^-10 mm/s to less than 3 years for a growthrate of 5 x 10^-10 mm/s based on crystal size distributions.The origin of crystal clusters is likely to involve either (ora combination of) heterogeneous nucleation, remobilization ofcumulate mushes or crystals sticking together during settlingand/or flow. The spatial distribution pattern of clustered crystalframeworks from both natural and experimental examples constrainsfields on spatial packing diagrams that allow the identificationof touching and non-touching crystal populations, and furtherimprove our understanding of crystal packing arrangements andcluster size distributions. KEY WORDS: cumulates; CSD; komatiite; basalt; spatial packing; textural analysis     

Textural history of recent basaltic-andesites and plutonic inclusions from Merapi volcano

Mt. Merapi in Central Java is one of the most active stratovolcanoes on Earth and is underlain by a multistage plumbing system. Crystal size distribution analyses (CSD) were carried out on recent Merapi basaltic-andesites and co-eruptive magmatic and plutonic inclusions to characterise the crystallisation processes that operate during storage and ascent and to obtain information on respective time scales. The basaltic-andesites exhibit log-linear, kinked-upwards CSD curves for plagioclase and clinopyroxene that can be separated into two main textural populations. Large plagioclase phenocrysts (≥1.6 mm) make up one population, but correspond to crystals with variable geochemical composition and reflect a period of crystal growth at deep to mid-crustal levels. This population was subsequently influenced by crystal accumulation and the onset of crustal assimilation, including the incorporation of high-Ca skarn-derived xenocrysts. Textural re-equilibration is required for these crystals to form a single population in CSD. A second episode of crystal growth at shallower levels is represented by chemically homogenous plagioclase crystals <1.6 mm in size. Crustal assimilation is indicated by, for example, oxygen isotopes and based on the CSD data, crystallisation combined with contamination is likely semi-continuous in these upper crustal storage chambers. The CSD data observed in the basaltic-andesite samples are remarkably consistent and require a large-volume steady state magmatic system beneath Merapi in which late textural equilibration plays a significant role. Plagioclase CSDs of co-eruptive magmatic and plutonic inclusions may contain a third crystal population (<1 mm) not found in the lavas. This third population has probably formed from enhanced degassing of portions of basaltic-andesite magma at shallow crustal levels which resulted in increased crystallinity and basaltic-andesite mush inclusions. A suite of coarse plutonic inclusions is also present that reflects crystallisation and accumulation of crystals in the deep Merapi plumbing system, as deduced from CSD patterns and mineral assemblages.     

粤北大宝山矿区加里东期火山岩的厘定及其地质意义

粤北大宝山矿区一带出露一套与层状Fe-Cu-Pb-Zn矿化紧密共生的层状火成岩。层状火成岩产状与上覆页岩及大理岩和下伏碳质页岩基本一致。本文通过层状火成岩显微特征及锆石年龄探讨火成岩形成环境及时代。层状火成岩为斑状结构,块状构造,局部发育条带状构造及流动构造。层状火成岩的斑晶主要由火山喷发形成的棱角明显石英、斜长石、钾长石、少量角闪石、黑云母及黄铁矿等晶屑及少量岩屑组成,基质为火山熔浆凝结形成的全晶质矿物,主要由粒度极细的石英、钾长石、绢云母、白云母及少量黑云母等组成,石英和钾长石构成典型的霏细结构。层状火成岩含大量火山碎屑及具流动构造等现象表明其为火山碎屑熔岩类,主要为英安质凝灰熔岩、流纹质凝灰熔岩及角砾熔岩。大宝山矿区中部流纹质凝灰熔岩和东部丘坝一带英安质凝灰熔岩的锆石LA-ICP-MS U-Pb年龄分别为436.4±4.1Ma,MSWD=0.94和434.1±4.4Ma,MSWD=1.9,是加里东期形成的。据大宝山矿区熔岩锆石U-Pb年龄,结合层状熔岩和灰岩及碳质页岩紧密共生及区域深大断裂构造活动特征,我们认为大宝山与层状矿化关系密切的层状火成岩为加里东期海相火山熔岩,粤北一带加里东期海相火山活动可能和形成于加里东期的吴川-四会深大断裂活动有关。     

Crystal Size Distribution of Plagioclase and Amphibole from Soufriere Hills Volcano, Montserrat: Evidence for Dynamic Crystallization-Textural Coarsening Cycles

The crystal size distributions (CSDs) of plagioclase and amphibolewere determined from andesites of the Soufrière Hillsvolcano, Montserrat. Plagioclase occurs as separate crystalsand as chadocrysts in large amphibole oikocrysts. The chadocrystsrepresent an earlier stage of textural development, preservedby growth of the oikocryst. Seventeen rock and eight chadocrystplagioclase CSDs are considered together as a series of samplesof textural development. All are curved, concave up, and coincident,differing only in their maximum crystal size. Three amphiboleCSDs have a similar shape and behaviour, but at a differentposition from the plagioclase CSDs. A dynamic model is proposedfor the origin of textures in these rocks. Crystallization ofplagioclase started following emplacement of andesite magmaat a depth of at least 5 km. A steep, straight CSD developedby nucleation and growth. This process was interrupted by theinjection of mafic magma into the chamber, or convective overturnof hotter magma. The magma temperature rose until it was buffered,initially by plagioclase solution and later by crystallization.During this period textural coarsening (Ostwald ripening) ofplagioclase and amphibole occurred: small crystals dissolvedsimultaneously with the growth of large crystals. The CSD becameless steep and extended to larger crystal sizes. Early stagesof this process are preserved in coarsened amphibole oikocrysts.Repetitions of this cycle generated the observed family of CSDs.Textural coarsening followed the ‘Communicating Neighbours’model. Hence, each crystal has its own, unique growth–solutionhistory, without appealing to mixing of magmas that crystallizedin different environments. KEY WORDS: Ostwald ripening; textural coarsening; oikocryst; CSD; texture