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.
This is cloud. They are usually white by irregular reflection . Rain cloud is dark because their water drops are rather large and less transparent. There are many chances when cloud is formed. For example towering thundercloud is formed when air rises high up in the sky. ( I am Japanese and I am afraid my answer may be difficult to understand and contain grammatical errors.) Source(s):