The rare earth elements, lanthanum to lutetium (atomic numbers 57—71), are members of Group IIIA in the periodic table (Fig. 1.1) and all have very similar chemical and physical properties. This uniformity arises from the nature of their electronic configurations, leading to a particularly stable 3+ oxidation state and a small but steady decrease in ionic radius with increase in atomic number for a given co-ordination number. Despite the similarity in their chemical behaviour, these elements can be partially fractionated, one from the other, by several petrological and mineralogical processes. The wide variety of types and sizes of the cation co-ordination polyhedra in rock-forming minerals provides the means for this chemical fractionation: it is this phenomenon which has important consequences in geochemistry <...>

Geochemists recognize the utility of the rare earth elements (REE) as especially powerful tools for tracing geochemical processes within the earth. Interest in the REEs reflects, in large part, their unique and chemically coherent properties that arise as a result of their trivalent charge and the similar ionic radii of all 14 naturally occurring rare earths. For example, owing to their trivalent charge, the REEs are chemically fractionated from divalent Ba and tetravalent Hf, their nearest neighbors in the Periodic Table of the Elements.

Garnets occur in more than 30 natural mineral parageneses forming the rocks of magmatic, metamorphoric and metasomatic origin, which suggests their crystallization in a wide range of physicochemical parameters. By the ratio of main components (Ca, Mg, Al, Fe, Cr, Mn), garnets are divided into two major groups: almandine (pyrope, almandine, and spessartite) and andradite (grossular, andradite, and uvarovite). Pyropes are contained mainly in high-temperature peridotites and eclogites from deep xenoliths carried by kimberlite and alkaline-basaltic melts. In high-temperature and mesobaric metamorphic complexes (eclogites, granulites, gneisses, and schist), as well as in metasomatic rocks (skarns) garnets are represented by the varieties of almandine-grossular-pyrope series. When systematizing garnets by chemical compositions and parageneses in which they occur, normally different binary diagrams are used, including the diagrams in CaO–Cr2O3 coordinates [Sobolev, 1964; Sobolev et al., 1973]. <...>

Редкоземельные элементы. Новый подход к взаимосвязи спроса, предложения и использования: на примере использования неодима в постоянных магнитах

Rare earth elements (REE) have gained enormous economic, public and increasingly scientific interest in the few recent years. Numerous headlines have appeared during the last about 4 years dealing with REE in the news and newspapers around the world, in press announcements, as short informational letters as well as numerous reports and studies from  onsultants, think tanks and governmental research groups. The vastness of the reports could lead to the conclusion that all has been said about REE, that the problems have been identified and the actions to be taken are known.