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.
Cirrus clouds are a high-level cloud (above 20,000 ft.), and they are made of icy crystals. These wispy, delicate-looking clouds arrive in advance of frontal systems, so they indicate the weather is about to change.