Experimental syntheses of framboids - a review

\Eleven reported laboratory syntheses of pyrite framboids are critically reviewed. Pyrite framboids are defined as microscopic spheroidal to sub-spheroidal clusters of equidimensional and equimorphic pyrite microcrystals. The synthetic products from the reported studies are critically reviewed based on this definition. Three of the reported studies have produced well-developed, large pyrite framboids clearly comparable to the natural varieties. Although many other studies claimed successful syntheses of pyrite firamboids, they did not report the textural and structural details of the products, which are necessary for the identification. Some of the products are described as pseudo-framboids which consist of a massive internal part with a microcrystalline surface layer, indicating a different formation process from that of framboids. Thus, careful structural examinations are required for reliable identification of synthetic pyrite spherulites. The common factor in the successful syntheses of pyrite framboids is extremely high supersaturation so that the pyrite nucleation rate is significantly greater than the crystal growth rate. Such conditions can be achieved by the addition of S(0), O-2 or by increasing Eh of the systems and by increasing temperature. (c) 2005 Elsevier B.V All rights reserved.