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.
A thunderstorm is a storm where you hear thunder and see lightning. Usually there is heavy rain in a thunderstorm. Thunderstorms are electric storms. When there is about to be a thunderstorm, a cumulonimbus cloud forms, often in a clear blue sky. (When a cloudâs name ends in nimbus, it means rain or snow is falling from the cloud.) The cloud increases in size and begins to build up peaks, which become very dark.