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.
At levels below 2,000 metres the clouds are the ones that appear grey in the sky-often the sort associated with an overcast day and quite likely to contain water which falls as rain. Typical cloud types are nimbostratus and stratocumulus.t levels below 2,000 metres the clouds are the ones that appear grey in the sky-often the sort associated with an overcast day and quite likely to contain water which falls as rain. Typical cloud types are nimbostratus and stratocumulus.