An element is one of the 92 naturally occurring substances composed of a single type of atom. Elements are bonded together by ionic, covalent, metallic or hydrogen bonds to form molecules. Minerals must have a solid crystalline structure . Some materials, such as obsidian and water, are non-crystalline. They are thus mineraloids .
Water is also a liquid.
Each is a mineral, even though they have the same chemical composition. Luster is a term applied to describe the freshly broken surface of a mineral. The main divisions are between metallic and nonmetallic. Nonmetallic luster may be further subdivided into pearly and resinous. Table 1 describes several common luster types and mineral examples.