Many [crystalline] minerals occur as incomplete and imperfect crystals that are grouped together in various arrangements. If these incomplete crystals are arranged around a common center like the spokes of a wheel, they are said to be radial or radiated. If the groups of incomplete crystals look like bundles of strings or fibers, they are described as fibrous. If they are in rounded masses that resemble bunches of grapes, they are called botryoidal. If they look like fish scales, they are described as scaly. Some crystalline minerals are made up of tiny grains that are grouped together like the grains in a lump of sugar. A mineral occurring in this way is described as [granular]. More descriptions of crystalline minerals are found in the section on Texas rocks and minerals (pp. [43]-98).
[Barite] specimen showing radial form.
[Amorphous] Minerals
An [amorphous] mineral, unlike a [crystalline] mineral, does not have a definite, orderly arrangement of its atoms. Because of this lack of internal structure, the mineral occurs in masses that have no regular geometric shapes, and it has no crystal form of its own. Only a few minerals are amorphous.
SOME DISTINGUISHING PROPERTIES OF MINERALS
We use our senses of sight, hearing, smell, touch, and taste to become aware of the world around us. For example, we recognize a flower by noting its color, its fragrance, and the texture, shape, and arrangement of its petals. These are some of its characteristic properties. A mineral also has distinguishing properties, among them color, luster, and hardness, which help us identify it. Some minerals have a single outstanding property, such as the magnetism of [magnetite], that makes them easier to recognize. But to identify most minerals, we need to determine not just one, but several properties.
[Chalcedony] showing botryoidal form.