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Recently it has been found in two different locations in South Eastern Desert of Egypt that some pegmatitic veins which invaded in gneissic rocks are associated with Yttrium bearing garnets with the general chemical composition c(3)a(2)d(3)O(12) The-concentration of Yttrium in these garnets reached 10,000 ppm. Garnets with lower concentration up to 300 ppm were also found in south Sinai peninsula, and are associated with metamorphosed sedimentary rocks. Both locations are part of the Arabo-Nubian Shield, and were mapped using Landsat images (TM) and extensive field work. In the present study our main concern was to determine the cation site population and chemical composition of all samples. Two different garnets structure models were identified. The typical occurrence of spessartine, almandine and pyrope were present and confirm the site population.