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Bulk chemistry and mineralogy of the peculiar rock of Ricetto (Carseolani Mts., Central Apennines, Italy) was studied to resolve its controversial origin: igneous dyke or anthropic product. This hybrid rock consists of a colorless, felsic component made up of glass plus quartz, and a brown, femic component made up of fans and spherulites of diopside, calcic plagioclase, wollastonite, and melilite. Textural relationships indicate very rapid cooling and immiscibility phenomena. The bulk chemistry of the rock is the same as that of the surrounding siliciclastic sandstone. The 14 C analysis of a coal fragment from bottom of the body yields the conventional age of 227(€50) years. The Ricetto occurrence is an example of pyrometamorphism of a siliceous limestone induced by a charcoal pit burning. The small size of the heat source at Ricetto caused an intense but short-lived melting of the country rock. Prograde metamorphism caused a temperature increase up to 1,000-1,100 C when melilite crystallization conditions were reached at appreciable P(CO 2 ) and high f(O 2 ). Melting occurred in a close system represented by the simplified equation: 3Cal+16.5Qtz+Ms+Bt!Mel+Melt+2H 2 O+ 3CO 2 +0.5O 2 . Diopside+calcic plagioclase+wollastonite formed by melilite breakdown during rapid cooling, through the reaction: 6Mel+6Qtz+0.5O 2 !3Di+2An+ 7Wo. Liquid immiscibility caused the separation between the felsic melt component and the femic melilite-bearing component. Immiscibility was characterized by different fractionation of alumina and alkalies between these two phases. Differences in bulk, glass, and mineral chemistry between the Ricetto and other melilite-bearing pyrometamorphic rocks can be attributed mainly to different protoliths.

The bimodal rock of Ricetto consists of a felsic glassy component, which prevails volumetrically at the top of the rock, and mafi c spherules of acicular diopside + anorthite + wollastonite pseudomorph after melilite, which are concentrated at the bottom of the rock. This texture clearly indicates liquid immiscibility, which can be modeled in the compositional space SiO 2 -Al 2 O 3 -MgO-CaO and Al 2 O 3 -CaO-(FeO T + MgO). The spinifex and dendritic forms are due to quenching from a melt at temperature of 1000-1100 °C: melilite was the fi rst phase to crystallize and the subsequent rapid cooling caused its breakdown to a more stable assemblage. The strict chemical similarity between the rock under study and the surrounding siliciclastic sandstones, together with the results of 14 C radiometric analysis on coal fragments found at bottom of the convex central part of the body, demonstrate that the rock of Ricetto is a man-made pyrometamorphic product. The genetic attribution of the Colle Fabbri occurrence to pyrometamorphic phenomena somewhat similar to Ricetto is diffi cult to be asserted, as the crystallization history at Colle Fabbri has been much more complicated than at Ricetto. The common presence of melilite and wollastonite cannot account for a direct comparison between the Ricetto and Colle Fabbri rocks, as conspicuous mineralogic, petrologic, and geologic differences exist between these two occurrences.*

Due to an unfortunate error, Equations (1), (2) and (3) were incorrect as published in the article.The correct equations are printed below. ð2Þ ð3ÞThe online version of the original article can be found at http:// dx

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