The garnets in coronal metagabbro and coronal eclogite are more heterogeneous in composition than those in coesitebearing. Hornblende is the most common example of the group of silicates called amphibole. Hornblende is commonly found in metamorphic rocks such as schists and gneisses, and igneous rocks such as diorites and dacites. As prismatic crystals, to 10 cm, and as rims on pyroxenes. 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.
In contrast metagabbro lacks olivine and exhibits textures that range from relict. Data collated from the literature on calcic amphiboles from other plutonic complexes and from phase equilibrium experiments using natural rocks or. 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. Granite, a light coloured, medium to coarsegrained intrusive rock, consists mainly of quartz, alkali and plagioclase feldspars, and micas. Pdf geochemistry and petrogenesis of elfringa metagabbro. This is the first examination of intrusive rocks you will make. Hornblende amphibole hornblende rocks are mostly types of metamorphic rocks. Pdf mineral and chemical composition and genesis of.
Mineral and chemical composition and genesis of hinis metagabbro eastern anatoliaturkey article pdf available in geochemistry international 463. Its color varies from darkbrown to darkgreen, appearing black from a distance as most mafic minerals. Gabbro is widely used as crushed stone for concrete aggregate, road base material, and railroad ballast. Secondary minerals are horn blende, actinolitic hornblende, ferich phlogopite, and vermiculite.
The four endmembers and the cation content of their respective compositions are as follows. Hornblende is frequently also used to describe any dark, opaque amphibole mineral without individual analysis. Metaperidotite, metapyroxenite, and hornblende metagabbro. Then determine the texture of the rock and based on the two, identify t he rock name. Essential minerals these are minerals that are required within the classification of this rock.
Hornblendes generalized chemical formula is ca,na2mg,fe,al5al,si8o22 oh2. How do you distinguish metamorphic amphibole from magmatic. The individual hornblende minerals appear very similar and can be virtually indistinguishable. The four endmembers and the cation content of their respective compositions are as. The rocks have the composition of ferriferous metagabbro. After that, we will do trace element analysis using ion or laser microprobe. Here are samples from a pleistocene andesite at mt. 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. In most cases, clinopyroxene in the metagabro is pseudomorphed by amphibole, rare cases relict clinopyroxene occurs within its core. 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. 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. Hornblende, calciumrich amphibole mineral that is monoclinic in crystal structure. A generally deeper level of contact metamorphism at pressures of a few kilobars is represented by the hornblendehornfels facies. Plagioclase is highly altered and contains inclusions of secondary minerals in it.
Replacement of pyroxene by hornblende, isochemically. Valid species bold all minerals that are ima approved or were considered valid prior to 1959 are in bold type. Tonalite, diorite, gabbro, norite, and anorthosite these intrusive plutonic rocks correspond to fields on diagram 22 of winter. Hornblende is the most common of the clinoamphiboles. We are just going to do electron microprobe analysis of minerals ol, hbl, px, plg. 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. Infiltrationdriven dehydration and anatexis in granulite. 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.
Hornblenderich, high grade metamorphic terranes in the southernmost sierra nevada, california, and implications for crustal depths and batholith roots donald c. The core was drilled for lasir gold in january 1988. Hornblende is a group name used to describe ferrohornblende and magnesiohornblende, but the term is generally more inclusive for all calcium aluminum amphiboles. A sample of hornblendebiotite granodiorite gneiss yielded a nd model age of c. The highest spessartine content occurs in coronal metagabbro figure 8. Hornblende s generalized chemical formula is ca,na2mg,fe,al5al,si8o22 oh2. Garnets are surrounded by thin coronas composed of plagioclase and symplectic intergrowths of plagioclasepyroxene. 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. Plagioclase consists of subhedral, lathshaped, tabular or blocky grains, typically mm in maximum direction. The specimen was once in charles hoadleys collection, who assembled one the best collections in american history during the early 1900s. These samples of hornblende are displayed in the smithsonian museum of natural history. Other articles where hornblendehornfels facies is discussed.
First determine composition, which is based on mineral content or color, if you cant see minerals. Composition quartz potassium muscovite biotite hornblende plagioclase pyro feldspar xene olivine color index if cant see minerals. Gabbroic rocks contain plagioclase, olivine, orthopyroxene, clinopyroxene, hornblende, and biotite, and. Pdf ironcopper mineralization associated with metagabbro in. Metamorphosed gabbro from tsundupalle greenstone belt, eastern dharwar craton contain clinopyroxene cpx and plagioclase pl as primary minerals. A variety of techniques are available for calculating gains and losses of elements during metasomatism from the chemical analyses of the respective rocks. Average composition of zircons sc1 rorb29a sio 2 32.
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. Hornblende for a hornblende this is a nice wellformed crystal arrangement. 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. 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. Precambrian metagabbro cordova mines, southeast ontario, canada. Metapyroxenite and metagabbro undifferentiated the delaware. Hornblende is a complex inosilicate series of minerals ferrohornblende magnesiohornblende. Hurlbut, cornelius s klein, cornelis, 1985, manual of mineralogy, 20th ed. The clinopyroxene is all augite with an average composition of en 46 tables t4, t7. Darkgreenishgray, coarse grained, massive, hornblende metagabbro. 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. 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.
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. Its composition is variable and its general formula is ca,mg,alsi 8 o 22 oh 2. 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. These rocks become finer grained and darker as hornblende replaces some of the. Gabbro is sometimes called black granite for it too is coarsegrained, but a large proportion of ironbearing minerals make gabbro heavier and dark colored. Petrology of the mecklenburg gabbrometagabbro complex, north. The individual hornblende minerals appear very similar and can be virtually indistinguishable without complex analysis. A coarsegrained plutonic rock composed essentially of calcic plagioclase, pyroxene and iron oxides. Hornblende, like other members of the amphibole group, is a common rockforming mineral. Hydrated phases become stable, and the transition to regional metamorphism becomes apparent.
A gabbro with plagioclase and hornblende with pyroxene. The metagabbro is het erogeneous in composition andor in particle size from microscopic to pegmatitic and shows modally graded rhythmic layering toksoy, 1998. Hornblende gneiss gneiss is a widespread metamorphic rock that is medium to coarse grained and often contains significant amounts of quartz and feldspar. Pronunciation icon sound file courtesy photo atlas of minerals. Disequilibrium texture and compositional relation of ca. 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 sample at left is about 12x8 cm and is from ontario, canada.
Lithos, 17 1984 247258 247 elsevier science publishers b. Pyrope content increases from coronal metagabbro, via coronal eclogite to coesitebearing eclogite. The mineral assemblage is typically dominated by plagioclase. Petrology of the mecklenburg gabbrometagabbro complex. To link to this object, paste this link in email, im or document to embed this object, paste this html in website. The general metasomatic equation derived by gresens 1967 supersedes all others because of its general applicability to all conditions of metasomatism and through its introduction of corrections for. Incorporation of metagabbro as cement replacement in. 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.
Mineral image icon mineral image is present for this mineral. The kurangah metagabbro, characterized by phlog opite, has clinopyroxene, hornblende, and plagioclase as primary minerals as well. The garnets in three types of rocks show different compositional ranges figure 8. Hornblenderich, high grade metamorphic terranes in the. 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. It looked like many of the other mineral ores which could be smelted to produce metals, but hornblende failed to be smelted. 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. This book aims to give a modern introduction to the study of opaque. The actinolitehornblende series in metabasites and the so. Metaperidotite, greenishblack, darkyellowish brown weathering, mediumgrained, massive. The hornblendeplagioclase hornfels from the contact. In general metagabbro is slightly higher in tio 2, na 2 o, and k 2 o, and lower in mgo relative to gabbro. Garnets are surrounded by thin coronas composed of plagioclase and symplectic intergrowths of.
Coexisting amphiboles from the noranda area, quebec. Abrupt and discontinuous changes in the composition of or the disappearance ofa mineral phase results in a marked composition gap between actinolite and hornblende. The specimen was once in charles hoadleys collection, who assembled one the best collections in american history. More information about these rocks is included in chapters 11, and 14 of moorhouse. Please see the mineralogical record archive about charles hoadley.
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