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: Tall and dark, often called thunderheads, accompanied by severe weather such as lightning, wind, and heavy precipitation (tends to be brief but intense). Thunderstorm clouds, officially called cumulonimbus clouds, also can produce hail, and they're the only clouds that can.