An anion is the element or ion that makes up the negatively charged part of a molecule. The definition of a mineral has six parts. If a substance fails to meet one of these criteria, then it cannot be classified as a mineral. Some substances that fail one or two of these conditions may be called mineraloids to distinguish them from minerals. There are other characteristics that define a mineral, but these other characteristics do not show up during a casual visual examination of the specimen.
Color can be a misleading characteristic of a mineral.
As you walk through the museum, notice that some minerals like fluorite, calcite, smithsonite and quartz come in a variety of colors. Despite the difference in color, fluorite is fluorite, calcite is calcite and quartz is quartz. The internal structure of a mineral is dependent on the arrangement on the atomic level. The external shape can be influenced by several factors including the internal arrangement of atoms, mode of formation and environment of crystallization. Twinning is common to some minerals.