Width of rock 8 cm. TUG There are only three common minerals among pyroxenoids wollastonite, rhodonite, and pectolite but even these are found in few rock types that are not very voluminous. Wollastonite as a most important of these minerals occurs only in a handful of places where it is abundant enough to make mining worthwhile.
One of them is Willsboro in New York State two photos below. It forms when limestone reacts with silicate fluids:. Wollastonite may form when impure contains silica limestone or dolostone gets buried deep enough for the necessary metamorphic reactions to take place regional metamorphism or when magmatic fluids intrude the limestone body metasomatism which produces skarns.
In either case many other minerals may form as well. Diopside , calcite, dolomite , tremolite, andradite , grossular, plagioclase, epidote , vesuvianite , etc. It may be very rarely found in some igneous rocks. Fabrice Brunet. Matthieu E. Select Format Select format.
Permissions Icon Permissions. Abstract In the Alpine blueschist- to eclogite-facies meta-ophiolitic units of northern Corsica, the contact between a serpentinite body and an immediately overlying siliceous marble is remarkable for the occurrence of wollastonite and, on the marble side, a dark halo around the serpentinite.
A clue to its origin is the abundance of graphitic matter with the wollastonite within a few decimetres of the serpentinite body. We interpret this observation as evidence for local reduction of Ca-carbonate to form elemental carbon and wollastonite according to the reaction. Open in new tab Download slide. Table 1: Garnet and clinopyroxene composition in serpentine and the reaction zones. Open in new tab. Table 2: Serpentine, chlorite, balangeroite, wollastonite, carbonate, mica and talc composition in serpentinite and the reaction zones.
One of the most striking observations in the contact zone is the abrupt disappearance of calcite coupled with the appearance of graphitic matter GM and wollastonite to form a marked dark reaction zone Z3.
The reaction front is c. Lath-shaped crystals of wollastonite seem to replace calcite Fig. The size of the wollastonite grains increases towards Z2 concomitantly with GM content Fig. We take all these observations, in particular the coincidence of carbon enrichment the dark halo with wollastonite appearance and calcite disappearance, as compelling evidence that zone Z3 arose from the progression of the following decarbonation reaction into the original marble, by which carbonate is reduced directly to produce elemental carbon:.
The chemical profile from marble to serpentinite provides an answer to the question left pending by Chopin et al. Potassium, which is absent from the reaction zone Fig. At the zone Z3—marble contact, white mica is surrounded by garnet Fig. Actually, in zones Z2 and Z3 where white mica is now absent, garnet displays lamellar morphologies mimicking a mica habit Fig. The combination of textural and chemical information with respect to potassium therefore suggests that the disappearance of white mica is coupled to potassium leaching and garnet growth, and to the unusual conditions prevailing near the contact with the serpentinite.
On this basis and taking Ca-carbonate reduction into account, a tentative dissolution reaction can be proposed as follows:. The redox conditions modelled here and the areal distribution of the wollastonite—GM halo point to the reducing effect of the serpentinite body during metamorphism. In the serpentinite the coexistence of Co-bearing pentlandite and magnetite is the only constraining assemblage with respect to oxygen fugacity.
Consequently, in the absence of Fe—Ni alloys, the ambient oxygen fugacity of the serpentinite is difficult to constrain. It is now well established that peridotites have a strong reducing potential Berndt et al. However, the reducing effect of a fully serpentinized body that could further interact with aqueous fluids i.
In addition to uvarovite—andradite garnet formation, for which thermodynamic data are lacking, a reaction that can account for the reducing potential of the serpentinite is the following serpentine—magnetite equilibrium:. The assumption of a reaction process dominated by diffuse transport rather than fluid advection underlies this study; it is apparently challenged by the potassium profile, which could suggest potassium leaching in the marble by aqueous fluid flow.
Potassium dissolution can be accounted for by reaction 2 , the equilibrium constant K E2 of which depends on the potassium, water and oxygen activities as well as the pH of the aqueous fluid, in addition to P and T , as follows:. Google Scholar Crossref. Search ADS. Rodingitization and hydration of the oceanic lithosphere as developed in the Leka ophiolite, north—central Norway. High-pressure behaviour of serpentine minerals: a Raman spectroscopic study.
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US Geological Survey Bulletin. Balangeroite, a new fibrous silicate related to gageite from Balangero, Italy. Multivariable phase diagrams; an algorithm based on generalized thermodynamics.
Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation. An automated strategy for calculation of phase diagram sections and retrieval of rock properties as a function of physical conditions.
Dal Piaz. Filoni rodingitici e zone di reazione a bassa temperatura al contatto tettonico tra serpentine e rocce incassanti nelle Alpi occidentali italiane.
In situ characterization of serpentinites from forearc mantle wedges: Timing of serpentinization and behavior of fluid-mobile elements in subduction zones.
Di Colbertaldo. Lizardite versus antigorite serpentinite: Magnetite, hydrogen, and life? A nickel—iron analogue of balangeroite and gageite Sasaguri, Kyushu, Japan. Etude structurale d'un cisaillement ductile: le charriage ophiolotique corse dans la region de Bastia.
Formation of wollastonite by chemically reactive fluid flow during contact metamorphism, Mt. The Geology of Gem Deposits. Thermodynamics of order—disorder in minerals: II. Symmetric formalism applied to solid solutions. An internally consistent thermodynamic data set for phases of petrological interest.
Feedbacks between mantle hydration and hydrothermal convection at ocean spreading centers. Documents du BRGM. The oxidation state of metasomatized mantle wedge: insights from C—O—H-bearing garnet peridotite. Evolutionary model for Alpine Corsica: mechanism for ophiolite emplacement and exhumation of high-pressure rocks.
Wollastonite formation during Variscan post-tectonic cooling in the Schwarzwald, Germany. Phengite geobarometry based on the limiting assemblage with K-feldspar, phlogopite, and quartz.
Cold subduction and the formation of lawsonite eclogite—constraints from prograde evolution of eclogitized pillow lava from Corsica. The catalysis of mineral reactions by water and restrictions on the presence of aqueous fluid during metamorphism. CH 4 inclusions in orogenic harzburgite: Evidence for reduced slab fluids and implication for redox melting in mantle wedge. Vitale Brovarone. Inherited ocean—continent transition zones in deeply subducted terranes: Insights from Alpine Corsica.
Coexistence of lawsonite-bearing eclogite and blueschist: phase equilibria modelling of Alpine Corsica metabasalts and petrological evolution of subducting slabs. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals. Issue Section:. Download all slides.
Supplementary data. Supplementary Data - zip file. View Metrics. Email alerts Article activity alert. Advance article alerts. New issue alert. In progress issue alert. Receive exclusive offers and updates from Oxford Academic. Related articles in Web of Science Google Scholar. Citing articles via Web of Science Wollastonite is a substitute for asbestos in floor tiles, friction products, insulating board and other materials because it is chemically resistant, inert and stable at high temperatures, and its acicular morphology improves flexural and tensile strength of the finished products.
In , plastics and rubber applications accounted for 30 to 35 percent of U. Global markets in for wollastonite were ceramics 30 to 40 percent , polymers 30 to 35 percent and coatings 10 to 15 percent. The remaining sales were for construction, friction products and metallurgical applications.
In , global production of refined wollastonite was estimated to be , to , metric tons. These five countries produced more than 97 percent of the wollastonite used worldwide. Wollastonite was named for W. Wollaston — , an English chemist and renowned mineralogist, who discovered palladium and rhodium though not wollastonite. The wollastonite industry is relatively new, with limited commercial production starting in the s and large-scale mining beginning only in the s.
Wollastonite is used to manufacture products ranging from wheel covers for cars to glazes on bathtubs.
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