赣东北高压变质岩的岩石类型、矿物组成与变质过程

赣东北高压变质岩包括含硬玉霓辉石钠长角闪片岩、含硬玉霓辉石石英钠长石岩、含霓辉石角闪石英钠长石岩、含霓辉石钠长角闪片岩、蓝透闪石石英钠长石岩、镁钠闪石石英钠长石岩等岩石类型，主要组成脏矿物为硬玉、霓辉石、镁钠闪石、蓝透闪石、镁角闪石、阳起石、石英、钠长石、金红石和榍石。研究表明，高压变质峰期后经历了近等温降压退变质过程。     

缅甸硬玉岩地区的热液型钠长石岩

产于俯冲带内的低温高压带的由单矿物构成的硬玉岩通常伴有钠长石岩,目前对于硬玉岩研究的关注度较高,而对于钠长石岩则相对较低,很少有相关论文报导.产于缅甸翡翠矿区的钠长石岩,经常与硬玉岩相伴而生,是良好的研究样品.钠长石岩的主要矿物成分是低温钠长石,其次含有硬玉、绿辉石、透辉石等辉石类矿物和钠透闪石、蓝透闪石、镁钠闪石等闪石类矿物,此外还有钠沸石等.钠长石沿着解理和裂隙交代硬玉,说明钠长石形成晚于硬玉岩.钠长岩中的主要组成矿物钠长石的形成温度小于300℃,且其形成压力小于0.5kb,推测是在硬玉岩抬升程中通过交代与沉淀作用形成.其内的透辉石有两种类型,一类可能是被交代的硬玉中的透辉石组分会渐进增加,最终形成透辉石.另一类是被绿辉石包裹的透辉石残留,其很有可能是早期来自地幔楔或者俯冲带岩石中的矿物残留,即异剥钙榴岩或辉石岩类,可以视作硬玉化绿辉石岩和硬玉化异剥钙榴岩的矿物学证据.热液型钠长石岩的存在进一步说明缅甸翡翠矿区钠化热液存在现象的普遍性与穿越性.     

缅甸玉石中的钠铬辉石,硬玉及其共生矿物的研究

提出缅甸各种玉石中硬玉及其共生矿物的物理、光学Ｘ坶数据。硬玉玉石为单矿物或多矿物结晶质集合体。在多矿物集合体中，硬玉与浅闪石、钠透闪石、透闪石、钠铬辉石和顽火辉石最紧密地共生。钠长硬玉基本上由钠铬辉石和含或有时不含闪石类或顽火辉石的铬铁矿／镁铬铁矿组成，但没有纯的硬玉。     

缅甸翡翠原石中角闪石族矿物的形成

缅甸是世界上优质翡翠的最重要产地,角闪石族矿物是缅甸翡翠中的常见矿物。对缅甸翡翠原石进行手标本、薄片偏光显微镜观察和电子探针测试,结果表明,翡翠原石组成矿物的形成顺序为岩浆锆石→热液锆石和硬玉→绿辉石→Ca质角闪石→Na-Ca、Na质角闪石→钠长石,岩石形成后受到后期应力作用使部分角闪石族矿物发生变形。Ca质角闪石形成后,晚期Na-Al-Si流体和富Ca、Mg和Fe的浅闪石发生反应,形成了Na-Ca质、Na质角闪石,包括钠透闪石,蓝闪石和镁铝钠闪石。随压力的降低,残余流体在早期形成矿物颗粒之间沉淀结晶出钠长石。矿物的化学成分和矿物种类及结构对翡翠的品质有重要影响,硬玉中的Cr及角闪石矿物的存在导致了翡翠绿色深浅的变化。组成矿物的形态及颗粒大小、排列的紧密程度,影响翡翠的质地和透明度等外观特征。     

中国夕卡岩矿床中的角闪石

文章综合分析研究了中国21个夕卡岩矿床中的130个角闪石的成分分析数据。根据夕卡岩类型及其伴生金属矿化的不同，把角闪石分为4大类：钙夕卡岩中的角闪石多属钙角闪石，包括绿钙闪石、铁角闪石、镁绿钙闪石、铁浅闪石、阳起石、铁阳起石、铁镁钙闪石和铁韭闪石等；镁夕卡岩中的角闪石以透闪石为主，局部有浅闪石或韭闪石；锰质夕卡岩中的角闪石有锰质阳起石、锰质透闪石、锰直闪石和锰镁闪石；碱质夕卡岩中的角闪石属钠-钙角闪石或钠角闪石类，包括钠透闪石、镁亚铁钠闪石、亚铁钠闪石、镁铝钠闪石和镁钠闪石。碳酸盐围岩和有关侵入岩的成分对角闪石的类型、成分及其伴生金属矿化起重要的作用。     

滇西双江县勐库地区退变质榴辉岩中闪石类矿物的成因研究

勐库地区新近发现的退变质榴辉岩中晚期退变质作用形成的闪石类矿物十分丰富,其携带了大量晚期退变质过程中的岩石成因信息。本文通过系统的矿物学研究,鉴定出了3期10种闪石类矿物,其中以镁钙闪石、镁角闪石、铁镁钙闪石、铁韭闪石、透闪石、阳起石等钙质闪石类为主,有少量冻蓝闪石、蓝透闪石等钠-钙闪石类。研究发现,随着退变质过程中时间的推移,角闪石的形成环境逐渐由还原环境向弱氧化环境、氧化环境演变。根据角闪石电子探针成分测试结果计算了相应的温度、压力条件。结合岩相学的资料,将退变质过程分为3期:(1)第1期早阶段为近等温降压过程(p=0.56~0.75 GPa,t=642~709℃),主要形成铁韭闪石、铁镁钙闪石、镁钙闪石;晚阶段为等温降压过程(p=0.39~0.56 GPa,t=619~642℃),主要形成镁钙闪石及少量镁绿钙闪石、铁韭闪石;(2)第2期为降温降压过程(p=0.23~0.42 GPa,t=460~610℃),主要形成镁角闪石、冻蓝闪石及铁角闪石;(3)第3期为近等温降压过程(p=0.09~0.31 GPa,t=350~420℃),主要形成透闪石、阳起石、蓝透闪石等。闪石类的成分变化反映了退变质榴辉岩从地壳底部的角闪石榴辉岩-高压麻粒岩相温压环境向中上地壳角闪岩相、绿片岩相温压环境的渐次退变质作用过程。这与昌宁-孟连构造带上印支期的碰撞造山作用、燕山期的区域性地壳伸展、喜马拉雅期的陆内造山运动具有较好的对应关系。     

内蒙古北部苏尼特左旗蓝片岩岩石学和年代学研究

在苏尼特左旗以南地区的中古生代造山带的混杂岩带内发现了以岩块形式出现的蓝片岩,其矿物组合为斜长石+阳起石+蓝闪石+绿帘石+榍石。蓝片岩化学成分说明由基性火山岩变质而成。矿物化学分析表明,蓝片岩中角闪石可分为钙质、钙钠质和钠质3类。钙质闪石均为阳起石,钙钠质闪石为蓝透闪石和冻蓝闪石,钠质闪石为蓝闪石和青铝闪石及少量镁钠闪石。利用Na(M₄)和Al^Ⅳ的含量推测本区钙质、钙钠质和钠质3类闪石的压力从0.3～0.7Gpa,表明蓝片岩相变质作用的压力约为0.7GPa。用化学反应限定蓝片岩的形成温度为200～375℃左右。⁴⁰Ar³⁹Ar同位素年代学测定蓝闪石的等时线年龄为383±13Ma(1δ)。这些结果进一步证实沿贺根山—苏尼特左旗南是一条中古生代的缝合线,其俯冲—碰撞的标志即为混杂岩带以及其中的蓝片岩。     

俄罗斯阿尔丹地块西部穆龙斯克杂岩体中的碱性交代岩

含紫硅碱钙石、镁钠钙闪石（钠透闪石－石棉）及蓝色办透闪石的碱性交代岩的形成首先是由硅酸和碱（Ｎａ２Ｏ和Ｋ２Ｏ的不同作用）的惰性及ＦｅＯ,ＭｇＯ,ＣａＯ和Ａｌ２Ｏ３的强烈活性决定的,含蓝色软透闪石和镁的钙闪石（钠透闪石－石棉）的交换岩是岩浆期后溶解演化的中期产物,而含紫硅碱钙石的交换岩却是其晚期的产物。     

滇西蓝片岩中的角闪石

滇西蓝片岩的原岩为玄武质岩石和泥质岩,其矿物组合分别为Cr(或Win)+Chl±Ab+Ph+Ep±Act+Sph±Qz和Gl+Ph+Alm+Tc+Act+Chl+Qz+Do。哀牢山蓝片岩中的闪石普遍具有成分分带,核心为蓝透闪石,边缘为阳起石。澜沧江带中的蓝片岩,其碱性闪石显示了一定的成分变化,既有青铝闪石、镁钠闪石,也有蓝闪石。另外,在滇西蓝片岩中,共存的碱性闪石和钙质闪石之间存在着较大的成分间断。澜沧江带蓝片岩的变质年龄为193Ma。     

缅甸翡翠矿物与自然类型

ＮａＡｌＳｉ２Ｏ６分子〉５０％称为硬玉。按杂质元素将硬玉分为纯硬玉,钙硬玉、铬硬玉、绿硬玉。依据硬玉亚种及结构变化,划分为四个自然类型和１１个硬玉岩类别以及与之相对应的１１个翡翠玉种。硬玉岩的成矿作用有两个系列：纯硬玉－钙硬玉和（纯硬玉）－铬硬玉－氟镁纳闪石系列。前者参与成矿的特征元素是钠和钙;后者是钠、铬、镁。从残晶矿物提供的证据分析：前者发生在基性蚀变岩中;后者主要发生在超基性基中。硬玉岩经受     

Mineralogy of New Caledonian metamorphic rocks

The chemistry and phase relations of calcic and sodic amphiboles in the Ouégoa blueschists are investigated. The first appearance of sodic amphiboles is controlled by bulkrock chemistry. Sodic amphibole appears first in weakly-metamorphosed pumpellyite metabasalts prior to the crystallization of lawsonite but does not crystallize in pelitic schists until the middle of the lawsonite zone; sodic amphibole continues as an apparently stable phase in rocks of all bulk compositions into, and throughout, the highest-grade rocks in the district. Calcic amphibole is widespread in metabasalts of the lawsonite and epidote zones and also occurs in metasediments of appropriate composition. Coexisting pairs of calcic and sodic amphiboles are common in metabasalts but they have also been found in some metasediments. A grunerite-riebeckite pair is described.Electron-probe analyses of 120 amphiboles from representative rock-types are presented in graphical form. Sodic amphiboles show an increased Mg/(Mg+Fe) ratio with increasing metamorphic grade. Sodic amphiboles in pelitic schists are ferroglaucophane in the lawsonite zone and crossite and glaucophane in the epidote zone. Sodic amphiboles in metabasalts are iron-rich crossites in weakly-metamorphosed rocks and more-magnesian crossites and glaucophanes in the lawsonite and epidote zones. The abrupt increase in Mg/(Mg+Fe) ratio in sodic amphiboles at the epidote isograd is attributed to the crystallization of epidote and almandine which take the place of lawsonite and spessartine of the lawsonite zone. Calcic amphiboles are fibrous actinolites in the lawsonite zone and grade with increasing Al and Na/Ca ratio into prismatic blue-green hornblendes (barroisites) in the upper epidote zone. In calcic amphiboles, increasing metamorphic grade effects the coupled substitution of (Na+Al) for (Ca+Mg) and a small increases in Fe/Mg ratio; octahedrally and tetrahedrally coordinated Al increases in an approximately 11 ratio. Both the calcic and the sodic amphiboles show an increase in A-site occupancy with increasing metamorphic grade. In two-amphibole assemblages Ti, Mn and K are concentrated in the calcic amphibole.The textural and chemical relations between coexisting calcic and sodic amphiboles are discussed. If the calcic and sodic amphiboles are an equilibrium pair then the data collected from the Ouégoa amphiboles gives a picture of a very asymmetric solvus in the system glaucophane-actinolite-hornblende, i.e. steep-sided to glaucophane and with a gentle slope to the calcic amphibole field; there is no indication of any termination of the solvus under the pressure-temperature conditions of crystallization of the Ouégoa schists.     

Coexisting Amphiboles from Blueschist Facies Metamorphic Rocks

Four pairs of associated calcic and sodic amphiboles from blueschistfacies metamorphic rocks were analyzed with the electron microprobeand studied by single-crystal X-ray diffraction techniques.Except for ranges in the ratios Mg/(Mg+Fe) and Fe³⁺/(Fe³⁺+Al+Ti),the sodic amphiboles are similar in chemical composition. Theamount of calcium in the M(4)-site ranges only from 0·18to 0·21 ion per formula unit. The calcic amphiboles,in addition to a range in Mg/(Mg+Fe), vary in Na/(Na+Ca) ratio(0·29–0·48). Three of the calcic amphibolescontain less than 1·5 calcium ions per formula unit,indicating a significant solid solution of sodic amphibole componentsin the calcic amphibole phase. The a and b unit-cell parametersof the calcic amphiboles decrease with increased content ofthe sodic component.     

Mineralogy,petrology, and phase relations of glaucophane-lawsonite zone blueschists from the Tavşanli Region,Northwest Turkey

Glaucophane-lawsonite facies blueschists representing a metamorphosed sequence of basic igneous rocks, cherts and shales have been investigated northeast of the district of Tav?anli in Northwest Turkey. Sodic amphiboles are rich in magnesium reflecting the generally high oxidation states of the blueschists. Lawsonite has a very uniform composition with up to 2.5 wt.% Fe₂O₃. Sodic pyroxenes show an extensive range of compositions with all the end-members represented. Chlorites are uniform in their Al/(Al+Fe+Mg) ratio but show variable Fe/ (Fe+Mg) ratios. Garnets from metacherts are rich in spessartine (>50%) whereas those from metabasites are largely almandine. Pistacite rich epidote is found in metacherts coexisting with lawsonite. Phengites are distinctly higher in their Fe, Mg and Si contents than those from greenschist facies. Hematites with low TiO₂ are ubiquitous in metacherts. Fe²⁺/Mg partitioning between chlorite and sodic amphibole is strongly controlled by the calcium content of the sodic amphibole and ranges from 1.1 for low calcium substitution to 0.8 for higher calcium substitution. The Al/Fe³⁺ partition coefficient between sodic amphibole and sodic pyroxene is 2.1. A model system has been constructed involving projections from lawsonite, iron-oxide and quartz onto a tetrahedron with Na, Al, Fe²⁺ and Mg at its apices. Calcite is treated as an indifferent phase. The model system illustrates the incompatibility of the sodic pyroxene with chlorite in the glaucophanelawsonite facies; this assemblage is represented by sodic amphibole. Sodic amphibole compositions are plotted in terms of coexisting ferromagnesian minerals. Five major areas on the sodic amphibole compositional field are delineated, each associated with one of the following minerals: chlorite, stilpnomelane, talc, almandine, deerite.     

The compositional variation of synthetic sodic amphiboles at high and ultra-high pressures

Sodic amphiboles in high pressure and ultra-high pressure (UHP) metamorphic rocks are complex solid solutions in the system Na₂O–MgO–Al₂O₃–SiO₂–H₂O (NMASH) whose compositions vary with pressure and temperature. We conducted piston-cylinder experiments at 20–30?kbar and 700–800?°C to investigate the stability and compositional variations of sodic amphiboles, based on the reaction glaucophane=2jadeite+talc, by using the starting assemblage of natural glaucophane, talc and quartz, with synthetic jadeite. A close approach to equilibrium was achieved by performing compositional reversals, by evaluating compositional changes with time, and by suppressing the formation of Na-phyllosilicates. STEM observations show that the abundance of wide-chain structures in the synthetic amphiboles is low. An important feature of sodic amphibole in the NMASH system is that the assemblage jadeite–talc?±?quartz does not fix its composition at glaucophane. This is because other amphibole species such as cummingtonite (Cm), nyböite (Nyb), Al–Na-cummingtonite (Al–Na-Cm) and sodium anthophyllite (Na-Anth) are also buffered via the model reactions: 3cummingtonite?+?4quartz?+?4H₂O=7talc, nyböite?+?3quartz=3jadeite?+?talc, 3Al–Na-cummingtonite + 11quartz + 2H₂O=6jadeite + 5talc, and 3 sodium anthophyllite?+?13quartz?+?4H₂O=3 jadeite + 7talc. We observed that at all pressures and temperatures investigated, the compositions of newly grown amphiboles deviate significantly from stoichiometric glaucophane due to varying substitutions of Al^IV for Si, Mg on the M(4) site, and Na on the A-site. The deviation can be described chiefly by two compositional vectors: [Na^AAl^IV]<=>[□^ASi] (edenite) toward nyböite, and [Na^(M4)Al^VI]<=>[Mg^(M4)Mg^VI] toward cummingtonite. The extent of nyböite and cummingtonite substitution increases with temperature and decreases with pressure in the experiments. Similar compositional variations occur in sodic amphiboles from UHP rocks. The experimentally calibrated compositional changes therefore may prove useful for thermobarometric applications.     

The Serra da Graciosa A-type Granites and Syenites, southern Brazil. Part 3: Magmatic evolution and post-magmatic breakdown of amphiboles of the alkaline association

Amphiboles are the main mafic minerals in most metaluminous to peralkaline alkali-feldspar granites and syenites, and they usually preserve an important record of the compositional evolution of the melts from which they crystallize. In the alkaline association of the Serra da Graciosa A-type Granites and Syenites (southern Brazil), amphibole compositions span a large range, including calcic, sodic–calcic, and sodic amphiboles. Calcic amphiboles are typically observed in the metaluminous rocks, while sodic amphiboles are characteristic of the more strongly peralkaline rocks; sodic–calcic amphiboles are found in intermediate varieties. Compositional variations record the differentiation trends within two petrographic series of the alkaline association. The overall evolution of amphibole compositions is similar in both: they reveal a progressive increase in Na and Fe³⁺ with differentiation (increase in alkalinity of the magmas), a characteristic shared by undersaturated peralkaline (or agpaitic) differentiation trends. In detail, however, the evolutions of the amphibole compositions in the two series are distinct. In Alkaline series 1, the cores of the crystals form a continuum from calcic to sodic compositions, with the exception of a small compositional gap within the sodic–calcic amphiboles. The rims, however, show compositions that diverge from this main trend; this divergence results from increasing amounts of the oxy-amphibole component, and reflects more oxidizing conditions at the final stages of magmatic crystallization. In Alkaline series 2, these oxidation trends are much more subtle and a reverse trend is observed in the sodic amphiboles. Sodic–calcic amphiboles are in several cases replaced by intergrowths of post-magmatic sodic amphibole and Al-poor (“tetrasilicic”) biotite.     

西南天山超高压变质带的两类石榴角闪岩

角闪岩是西南天山超高压变质带变基性岩的常见岩石类型之一.野外关系和矿物反应结构表明,大多数角闪岩是由榴辉岩或蓝片岩受到不同程度的钠长绿帘角闪岩相退变质叠加形成的.但对于一些平衡结构发育良好且孤立产出的角闪岩类型（如石榴角闪岩）仍缺乏系统的岩石学研究.本次从岩相学、矿物成分以及热力学模拟几个方面对哈布腾苏河下游地区超高压带内不含钠长石的石榴角闪岩开展了详细的工作.这些石榴角闪岩的主要矿物为绿色角闪石（钙质-钠钙质闪石）、帘石（黝帘石-绿帘石）和石榴石,三者总体积占80%~90%,明显有别于大多数由榴辉岩退变而成的含有钠长石变斑晶的石榴角闪岩.虽然这些角闪岩化学成分十分相近,都具有富钙贫钠和高的Mg/（Mg+Fe）比值,但在结构、构造和矿物组成等方面存在显著差异,据此将它们划分为两类.第一类角闪岩基质中不含石英,保存在变斑晶中的少量残余矿物组合为石榴石+绿辉石+硬柱石+蓝闪石+金红石,指示峰期硬柱石榴辉岩相变质条件,富钛矿物全部为金红石.第二类角闪岩强烈面理化,面理由绿色角闪石、绿帘石和绿泥石以及条带状石英集合体构成.石榴石粒度呈双峰式分布,粗粒比细粒低钙低锰.基质和包体中均未发现高压变质特征矿物绿辉石和蓝闪石.富钛矿物以榍石为主,金红石和钛铁矿仅存在于个别石榴石中.两类角闪岩的石榴石成分具有较大区分度,前者的钙含量较高而镁含量较低.P-T视剖面计算显示它们的峰期条件为480~520 ℃,30~33 kbar,均达到超高压范围,与哈布腾苏河下游及以西地区的榴辉岩相似,表明西南天山超高压变基性岩构成沿中天山南缘断裂延伸数十千米的独立地质单元,不存在所谓的俯冲隧道混杂现象.      

Sodic amphiboles and pyroxenes from fenites in East Africa

During alkali metasomatism of the country-rock associated with ijolite-carbonatite complexes the development of sodic amphibole and/or pyroxene is characteristic. In this paper, some new chemical analyses of these minerals, together with published analyses from fenites of Kenya, Uganda and Tanzania, include those of co-existing pairs of amphibole and pyroxene. The common amphiboles of the fenites are magnesioarfvedsonites with 100 Mg: Mg+Fe+Mn ranging from 67 to 36. They co-exist with aegirines having 0.75 to 0.89 ions Fe⁺³. Most of these minerals are poor in Ca; co-existing pairs tend to show corresponding increases in Ca and in Fe⁺². In the syenitic fenites of Tororo and Budeda, considered to have formed at higher temperatures, the stable mineral is aegirine-augite. New analyses of richterite, magnesioarfvedsonite and aegirine from carbonate-rich rocks are also presented, and the relation between fenites and carbonatites is discussed.     

The groundwater geochemistry in a semi-arid, fractured crystalline basement area of Dodoma, Tanzania

The chemical character of groundwater is generated through processes including the leaching of surficial and near-surface soil salts, cation exchange and mineral dissolution of, in this case, mainly amphiboles and sodic plagioclase. Molar ratios thermodynamic analysis using a NETPATH geochemical model and standard Piper trilinear and Gibbs diagrams have been used to establish these geochemical processes. Though the groundwater is dominantly of NaCl type, it is apparently suitable for general irrigation purposes.     

Coexisting amphiboles in an eclogite from the Western Alps: new constraints on the miscibility gap between sodic and calcic amphiboles

Abstract Crystal-chemical relationships between coexisting sodic and calcic amphiboles have been studied in eclogitic metagabbros from the Aosta Valley, Western Alps. Textural analysis gives evidence of three successive high-pressure parageneses:
1. Pre-kinematic high-grade blueschist assemblages, preserved as polymineralic inclusions in garnet cores and made of glaucophane and actinolite (stage A).
2. Synkinematic eclogite assemblages, composed of garnet + omphacite + glaucophane ± actinolite ± white mica ° Clinozoisite + quartz + rutile (stage B).
3. Post-kinematic epitactic overgrowths of barroisitic amphibole on glaucophane and actinolite (stage C).
P–T conditions of the eclogitic metamorphism have been estimated at around 500–550°C, 16 kbar.
Glaucophane and actinolite coexist as discrete grains in stage A and B assemblages. This texture and the chemistry of the amphiboles unambiguously denotes the existence of a miscibility gap between sodic and calcic amphiboles (from Na^M4= 0.80 in actinolite to Na^M4= 1.70 in glaucophane at T = 500–550°C). A comparison with published analyses allows a new solvus along the glaucophane–actinolite join to be drawn.
The later barroisitic amphibole (stage C) exhibits strong chemical zonation indicating disequilibrium growth. This amphibole cannot either be used to define a miscibility gap with glaucophane or actinolite or be considered as an intermediate stage between these two end-members.     

Amphibolitization of metagabbros in the Scottish Highlands

Abstract Compositions of actinolite, hornblende and cummingtonite, together with pyroxene and plagioclase, are studied in basic intrusions in the Dalradian of north-east Scotland, and the Glen Scaddle complex in the West Moine. Amphibolitization is due to influx of water from the country rocks. Pyroxene compositions are found to have adjusted to the regional metamorphic environment. Owing to the difficulty of diffusion of Al and Si, calcic amphiboles are zoned and commonly contain quartz blebs. Discontinuities in zoning give rise to actinolite-hornblende pairs. Compared with north-east Scotland, disequilibrium is less strong in the Glen Scaddle area: in the latter, plagioclase compositions have been greatly changed, Na partition between hornblende and plagioclase is close to equilibrium, the maximum Al content of hornblende is lower and zoning patterns are more consistent. The Fe/Mg ratio in calcic amphiboles varies with Al content, while approaching equilibrium partition with other minerals. Both zoning patterns and Fe/Mg partition with cummingtonite suggest that Fe/Mg of the calcic amphiboles increases more strongly with increasing (Al^vi+Fe³⁺) than can be explained simply by substitution of Al,Fe³⁺ for Mg on M2. Model reactions for amphibole formation are constructed. Cummingtonite formed at lower chemical potential of CaO than actinolite: Ca was exchanged for Mg,Fe between orthopyroxene-derived and clinopyroxene-derived local systems. Both cummingtonite and actinolite were formed because of kinetic constraints, as intermediate reaction products: actinolite-hornblende pairs represent disequilibrium. This work suggests that many occurrences of actinolite with hornblende, where the minerals are zoned, may also be due to diffusion kinetics.