The uppermost Paleozoic metaclastic sequences of the Pelagonian zone in northern Greece are connected to the western margin of the zone. They represent paleogeographic conditions of a deltaic environment and continental slope, which are related to the separation of the Paleozoic continent and the initial rifting in the western ophiolite belt in Greece. The metaclastic sequences define the western (external) boundary of the Pelagonian zone, and are used to find the continuation of this boundary in the Sporades and Oinouses islands in the Aegean Sea, in order to help answer the question of the connection between the Hellenides and the Taurides in Turkey.

ABSTRACT. A Ca-poor rhodonite (CaO 1.31 wt.%), found in a quartz vein cutting manganese ore bodies, north of the Xanthi plutonic complex (northeastern Greece) was studied. Microprobe analyses with optical and physical properties are given. The cell dimensions, obtained by least squares calculation from direct 0 value measurements on a Philips PW1100 single-crystal diffractometer are a = 7.626, b = 11.844, c = 6.702 A, ~, = 92.44 ~ = 94.28 ~ ~ = 105.70 ~ v= 579.89A 3, z = 10, and space group PI. R HOD O s I T E (Mn,Ca,Fe,Mg)SiO 3 is an important manganese mineral and occurs in Mn-bearing ore bodies as a result of metamorphic and commonly associated metasomatic activity. It also occurs as a rock-forming mineral of contact-metamorphosed calc-silicate rocks.It is well known that rhodonite always contains in varying amounts Ca 2+, Fe 2 +, and Mg 2+ substituted for Mn 2 +. The changes of mineralogical properties, due to cationic substitution, in rhodonire and related minerals have been well studied by Sundius (1931) and Tilley (1937), and particularly with respect to Ca content by Momoi (1964) with sixteen new analyses and a review of published data.The Ca content (1.31 wt.%) of the rhodonite from Xanthi area (northeastern Greece) is lower than the values so far cited for natural rhodonites. For this reason, and because this is the first description of rhodonite occurrence in Greece, we think that the study of this mineral is not without interest.Chemical data. Rhodonite never occurs as pure MnSiO3 but always contains a certain amount of divalent cations such as Ca 2+, Fe 2+, and Mg 2+ in substitution for Mn 2 +. The maximum contents of these elements reported in the literature for natural rhodonites are about 20, 26, and 15 mol. % as CaSiO3, FeSiO3, and MgSiO a respectively.Several electron probe analyses were performed on rhodonite crystals from Gorgona village, Xanthi, and the results, together with the number of ions calculated on the basis of eighteen oxygens, ~) Copyright the Mineralooical Societyare presented in Table I. The analyses were carried out partly in the Institute

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