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.
Cumulonimbus Clouds (thunderclouds). Cumulonimbus is a type of cloud that is tall, dense, and usually dark. These clouds form thunderstorms, and can create severe weather conditions, such as heavy rain, damaging winds, hail, lightning, and tornadoes. A cumulonimbus cloud that progresses to an intense, long-lived form is known as a supercell.