It is commonly called alumina, and may also be called aloxide, aloxite, or alundum depending on particular forms or applications. It commonly occurs in its crystalline polymorphic phase Î±-Al 2 O 3, in which it composes the mineral corundum, varieties of which form the precious gemstones ruby and sapphire.
rain cloud. (meteorology). Any cloud from which rain falls; a popular term having no technical denotation. 1  Facebook. 2  Twitter.
Cloud: a visible aggregate of tiny water droplets or ice crystals or a mixture of both suspended in the air. It forms when the condensation (or deposition) of water vapor meets supersaturation conditions (that is, relative humidity greater than 100%) within the air that is free of dust and other aerosols.