The individual hornblende minerals appear very similar and can be virtually indistinguishable. The garnets in coronal metagabbro and coronal eclogite are more heterogeneous in composition than those in coesitebearing. But can also be found in igneous rocks the rock is a middlegrade metamorphic rock, which means that it is formed under medium conditions of pressure and tempurature. How do you distinguish metamorphic amphibole from magmatic. The mineral assemblage is typically dominated by plagioclase. Metaperidotite, greenishblack, darkyellowish brown weathering, mediumgrained, massive. Hornblenderich, high grade metamorphic terranes in the southernmost sierra nevada, california, and implications for crustal depths and batholith roots donald c. Incorporation of metagabbro as cement replacement in. Hornblende, like other members of the amphibole group, is a common rockforming mineral. Hornblende for a hornblende this is a nice wellformed crystal arrangement. The four endmembers and the cation content of their respective compositions are as follows. Hornblendes generalized chemical formula is ca,na2mg,fe,al5al,si8o22 oh2. First determine composition, which is based on mineral content or color, if you cant see minerals. The garnets in three types of rocks show different compositional ranges figure 8.
The rocks have the composition of ferriferous metagabbro. Please see the mineralogical record archive about charles hoadley. Electronmicroprobe analyses of hornblendes from five calcalkaline plutonic complexes representing low and highpressure regimes define a tightly clustered linear trend in terms of total al alt and tetrahedral al aliv contents. Granite, a light coloured, medium to coarsegrained intrusive rock, consists mainly of quartz, alkali and plagioclase feldspars, and micas. Hornblende gneiss gneiss is a widespread metamorphic rock that is medium to coarse grained and often contains significant amounts of quartz and feldspar. Ten short lengths of drill core from the cordova mines gold deposit, selected from the drill core library at the ontario ministry of northern development and mines facility in tweed mndm, 1989. In most cases, clinopyroxene in the metagabro is pseudomorphed by amphibole, rare cases relict clinopyroxene occurs within its core. The sample at left is about 12x8 cm and is from ontario, canada. Petrology of the mecklenburg gabbrometagabbro complex, north. Quick navtop about hornblendebiotite granite classification subdivisions mineralogy internet links mineral andor locality is an outreach project of the hudson institute of mineralogy, a 501c3 notforprofit organization. Mineral and chemical composition and genesis of hinis metagabbro eastern anatoliaturkey article pdf available in geochemistry international 463. Home rocks and minerals hornblende hand specimen reference url share. After that, we will do trace element analysis using ion or laser microprobe.
The reduction in the normal consistency may be due to the mineralogical composition of metagabbro that is rich in hydrous silicate minerals such as hornblende, actinolite, and clinochlore, the former two minerals are of double chain structure, while the latter is of sheet structure beside its oily or soapy characteristic that decreases the. The specimen was once in charles hoadleys collection, who assembled one the best collections in american history. A sample of hornblendebiotite granodiorite gneiss yielded a nd model age of c. Its color varies from darkbrown to darkgreen, appearing black from a distance as most mafic minerals. Pyrope content increases from coronal metagabbro, via coronal eclogite to coesitebearing eclogite. This book aims to give a modern introduction to the study of opaque. Hornblende is a complex series of silicate minerals hornblende is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole it is an isomorphous mixture of three molecules. In general metagabbro is slightly higher in tio 2, na 2 o, and k 2 o, and lower in mgo relative to gabbro.
Hornblende, calciumrich amphibole mineral that is monoclinic in crystal structure. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Pdf geochemistry and petrogenesis of elfringa metagabbro. As prismatic crystals, to 10 cm, and as rims on pyroxenes. Gabbro is sometimes called black granite for it too is coarsegrained, but a large proportion of ironbearing minerals make gabbro heavier and dark colored. Hornblenderich, high grade metamorphic terranes in the. Plagioclase consists of subhedral, lathshaped, tabular or blocky grains, typically mm in maximum direction. The individual hornblende minerals appear very similar and can be virtually indistinguishable without complex analysis. Mineral image icon mineral image is present for this mineral. The four endmembers and the cation content of their respective compositions are as. Instead of breaking in broad, single cleavage planes like the micas, the cleavage surface of an amphibole mineral tends to display a large number of small, offset planes that help give the mineral a splintery appearance. Replacement of pyroxene by hornblende, isochemically.
Pdf ironcopper mineralization associated with metagabbro in. Plagioclase is highly altered and contains inclusions of secondary minerals in it. In a general sense, it is the intermediate type between basalt and rhyolite, and ranges from 57 to 63% silicon dioxide sio 2 as illustrated in tas diagrams. Data collated from the literature on calcic amphiboles from other plutonic complexes and from phase equilibrium experiments using natural rocks or. Hornblende is a common constituent of many igneous and metamorphic rocks such as granite, syenite, diorite, gabbro, basalt, andesite, gneiss, and schist it is the principal mineral of amphibolites. To link to this object, paste this link in email, im or document to embed this object, paste this html in website. Metagabbro is a metamorphosed variant of gabbro, the rock is also known as scapolite hornblende as the rock its self does not contain any feldspars as expected in gabbros but instead, the white minerals are scapolit with the dark greengrey mineral being hornblende. Average composition of zircons sc1 rorb29a sio 2 32.
The specimen was once in charles hoadleys collection, who assembled one the best collections in american history during the early 1900s. In fact, hornblende is the most prevalent of all the amphiboles. Hornblende is commonly found in metamorphic rocks such as schists and gneisses, and igneous rocks such as diorites and dacites. Hornblende is frequently also used to describe any dark, opaque amphibole mineral without individual analysis. Hydrated phases become stable, and the transition to regional metamorphism becomes apparent. Here are samples from a pleistocene andesite at mt.
We are just going to do electron microprobe analysis of minerals ol, hbl, px, plg. These samples of hornblende are displayed in the smithsonian museum of natural history. Gabbro is widely used as crushed stone for concrete aggregate, road base material, and railroad ballast. Hornblende is the most common example of the group of silicates called amphibole. Intrusive igneous rocks form where magma cools in a chamber below the surface of the earth, and because cooling as relatively slow, they tend to be coarsergrained than volcanic rocks. Infiltrationdriven dehydration and anatexis in granulite. Hurlbut, cornelius s klein, cornelis, 1985, manual of mineralogy, 20th ed. Garnets are surrounded by thin coronas composed of plagioclase and symplectic intergrowths of. The hornblendeplagioclase hornfels from the contact.
Tonalite, diorite, gabbro, norite, and anorthosite these intrusive plutonic rocks correspond to fields on diagram 22 of winter. This is the first examination of intrusive rocks you will make. Hornblende is the most common of the clinoamphiboles. Valid species bold all minerals that are ima approved or were considered valid prior to 1959 are in bold type. A coarsegrained plutonic rock composed essentially of calcic plagioclase, pyroxene and iron oxides. Very dark brown to black hornblendes that contain titanium are ordinarily called basaltic hornblende, from the fact that they are usually a constituent of basalt and related rocks. A variety of techniques are available for calculating gains and losses of elements during metasomatism from the chemical analyses of the respective rocks. Metapyroxenite and metagabbro undifferentiated the delaware. It looked like many of the other mineral ores which could be smelted to produce metals, but hornblende failed to be smelted. Then determine the texture of the rock and based on the two, identify t he rock name. Hornblende schist, for example, is a variety of schist rich in the amphibole mineral hornblende, though the rock may also contain an abundance of plagioclase feldspar and other substances as well. Darkgreenishgray, coarse grained, massive, hornblende metagabbro. A gabbro with plagioclase and hornblende with pyroxene.
A generally deeper level of contact metamorphism at pressures of a few kilobars is represented by the hornblendehornfels facies. More information about these rocks is included in chapters 11, and 14 of moorhouse. Pdf mineral and chemical composition and genesis of. Composition quartz potassium muscovite biotite hornblende plagioclase pyro feldspar xene olivine color index if cant see minerals. Pronunciation icon sound file courtesy photo atlas of minerals. Petrology of the mecklenburg gabbrometagabbro complex. Lithos, 17 1984 247258 247 elsevier science publishers b. Disequilibrium texture and compositional relation of ca.
Metaperidotite, metapyroxenite, and hornblende metagabbro. In contrast metagabbro lacks olivine and exhibits textures that range from relict. The name comes from a old german miners word, horn, which may be related to the color of horn, and the german word blenden, which means to deceive. Its composition is variable and its general formula is ca,mg,alsi 8 o 22 oh 2. Metamorphosed gabbro from tsundupalle greenstone belt, eastern dharwar craton contain clinopyroxene cpx and plagioclase pl as primary minerals. It generally occurs as batholiths and laccoliths and is often found along midocean ridges or in ancient mountains composed of compressed and uplifted oceanic crust. It has an average composition of an 51 table t4, but it varies widely because of zoning and background alteration table t8. Hornblende amphibole hornblende rocks are mostly types of metamorphic rocks. Coexisting amphiboles from the noranda area, quebec. Secondary minerals are horn blende, actinolitic hornblende, ferich phlogopite, and vermiculite. Hornblende s generalized chemical formula is ca,na2mg,fe,al5al,si8o22 oh2. Precambrian metagabbro cordova mines, southeast ontario, canada. Hornblende is a group name used to describe ferro hornblende and magnesio hornblende, but the term is generally more inclusive for all calcium aluminum amphiboles. The clinopyroxene is all augite with an average composition of en 46 tables t4, t7.
Hornblende is the major mineral of the amphibole group. Inrnooucrron described in the literature with an attempt to distinguish hornblende is the amphibole most commonly observed effects of p, t, fo, and bulk composition on the compoin calcalkalic granitoid rocks. The core was drilled for lasir gold in january 1988. The kurangah metagabbro, characterized by phlog opite, has clinopyroxene, hornblende, and plagioclase as primary minerals as well. Other articles where hornblendehornfels facies is discussed. In most other regards, gneiss is quite various and, therefore, is often named based on certain characteristics, such as parent material or mineral constituents, in order that samples of the. The actinolitehornblende series in metabasites and the so. Gabbroic rocks contain plagioclase, olivine, orthopyroxene, clinopyroxene, hornblende, and biotite, and. Darkgreen and white, massive to layered, coarsegrained equigranular metagabbro.
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