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The book summarizes the occurrence, geochemistry, mineralogy, petrology and phase-equilibria studies in air and under high pressures related to the most intriguing group of potassium-rich mafic and ultramafic rocks, often including host of exotic mineral assemblages including feldspathoids. Mantle-derived K-rich melts had intrigued most of the founders of Geology and many of the later experts in the field of Igneous Petrology, because they are sometimes associated with carbonatites and even diamond. They tend to contain anomalous concentration of many such elements as K, Rb, Sr, U, F, P, etc., along with Ni, Co and Cr indicating a mixture of crust and mantle materials. Although these rocks occur rarely in ancient geologic time, they have been erupting mostly in modern geological history (less than last 120 Ma or so). Are the old age data real or the result of a sampling problem? Modern observations leave no doubt that sediments must be subducted on a large scale. There is now evidence that the upper mantle (and perhaps even the lower mantle) is not homogeneous but rather like a fruit cake, and that there are thermal anomalies in the mantle resulting from deep mantle plumes or subduction. Is this related to release of these unusual rocks clearing the mantle of left over subduction materials? This volume, written for those interested in the geochemistry of K-rich melts from the deep Earth, reviews the present state of knowledge of these unique igneous rocks. The author is an expert in the field of Igneous Petrology and the book will serve as a valuable reference book for researchers and academicians in the discipline.

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Chapter 1. Introduction.- Chapter 2. Mineralogy.- Chapter 3. Classification.- Chapter 4. Different Localities of Potassium-Rich Silica-Undersaturated Igneous Rocks and their Silica-Rich Variants.- Chapter 5. Minor and Rare Earth Element Geochemistry of K-Rich Silica- Chapter 6. Undersaturated Igneous Rocks.- Chapter 7. Chemical and Physical Constraints for Crystallization of Feldspathoids and Melilite in Potassium-Rich Rocks.- Chapter 8. Ternary Systems with Feldspathoids.- Chapter 9. Incompatible Mineral Pairs in K-Rich Rocks.- Chapter 9. Leucite- and Feldspar-Bearing Systems.- Chapter 10. Melilite- and Leucite-Bearing Systems.- Chapter 11. Phase Relations in the System Leucite-Akermanite-Albite-SiO 2 .- Chapter 12. P-T Stability of Phlogopite, K-Richterite and Phengite, as a Source of Potassium in the Mantle.- Chapter 13. Experimental Studies on K-Rich Rocks.- Chapter 14. Structural and Tectonic Evolution of K-Rich Silica-Deficient Volcanic Provinces of Different Continents.- Chapter 15. Genesis of Ultrapotassic Rocks.- Chapter 16. Petrologic Conclusions.- References.

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