The most important indigenous sources, the destruction of which are large deposits of alluvial gem corundum are marbles and skarns rubinonosnye and sapfironosnye basalts. Rubinonosnye marbles and associated placer rubies spread over a vast area Mogokskogo mining area in the North. Burma and Thailand in a few areas. The largest sapphire developed in eastern Australia, Thailand and Cambodia, where they are indigenous sources - sapfironosnye basalts occupy a large area. Are also important sapfironosnye endoskarny, sapfironosnye plagioclasites and tremolitity in magnesian marbles. Relationship of some alluvial sapphire with skarns, developed at the contact with the syenite bodies of calcite-dolomite marbles, for example, is set in Sri Lanka. In Burma, the source of alluvial sapphire are "feldspar" strands, beneath which is probably implied. sapfironosnye plagioclasites, and in some cases - sapfironosnye syenitic pegmatites. The role of the crystalline schists and gneisses as a source of alluvial gem corundum is not entirely clear. Apparently, they are associated with relatively small alluvial deposits, such as known in the U.S. (North. Carolina), Zimbabwe and India. Due to metamorphic sources, probably formed glaciofluvial deposit of ruby and sapphire, recently discovered in Finland. Considerable industrial importance residual eluvial deposits of sapphire. They belong kaolinizirovannye by chemical weathering of ancient sapfironosnye tremolitity in magnesian marbles and calciphyres in Jammu and Kashmir (India), and giant dike sapfironosnaya lamprophyres in the main unit. Montana (USA). To the residual eluvial deposits of sapphires and rubies are also kaolinizirovannye plagioclasites and mica (phlogopite greisens) in serpentinite massifs of eastern Tanzania. The root is not affected by the process of chemical weathering of deposits of precious corundum is usually not developed because of the rock surrounding rocks is impossible to extract without damaging the quality crystals. Some exception is rubinonosnye mica, which, like the emerald, may be subjected to enrichment in order to extract the precious stone. Recently undertaken the development of an experimental primary deposits in northern Pakistan, related to rubinonosnymi marbles. In these fields, in contrast to the similar deposits of marble with disseminated mineralization in the ruby mining area Mogokskom Burma ruby forms large local concentrations suitable for use.