What are Minerals?
As simple as it may seem, this question sets the stage for our concern of trace minerals in human nutrition. Webster describes minerals as solid, crystalline substances (naturally occuring elements found in the earth), not of animal or vegetable origin. Important in this definition is the indication that their origin is not from animal or vegetable sources. Minerals for nutritional purposes cannot be synthesized by animals or plants. They must be utilized as natural elements from nature.
A mineral is a solid inorganic substance formed by geological processes. There are about 3,000 known minerals, and new discoveries occur frequently. All minerals have a specific atomic structure, chemical composition and physical properties. Minerals range from pure elements to salts to silicates that can take thousands of different forms. Gemstones are attractive minerals that have been cut and polished for use in making jewelry. Each mineral belongs to a chemical group that represents their affiliation with certain elements or compounds. Minerals also belong to a crystal structure group, and have other properties, such as hardness, color, luster, specific gravity, tenacity, and crystal habits associated with them. These and other properties are used to identify and classify them. A mineral’s crystal structure is important in determining its chemical and physical properties. A crystal structure refers to the way atoms are spatially arranged in the internal structure of a mineral. The
Solid Earth materials are made up of minerals and locally, their corresponding liquids. A mineral can be defined as: “a naturally occurring, inorganic, crystalline solid, with a fixed range of chemical composition and physical properties.” Minerals are chemical compounds composed of anions (e.g. oxygen – O-2) or anionic groups (e.g. carbonate – CO3-2) bonded to positively charged cations in a regular geometric atomic structure or lattice. An external expression of the atomic lattice of a mineral is the development of crystal faces. Crystals of different mineral have characteristic form or habit that reflects bond lengths, bond strengths, and inter-bond angles within the atomic structure. As a result, angles between equivalent faces of crystals for a given mineral have a constant value, as stated by Stenos Law. Because of this Constancy of Interfacial Angles, crystals exhibit varied degrees of symmetry, a repetition of the pattern of faces observed during manipulation of the crystal. Tw
Minerals are naturally occurring, inorganic solids with a definite chemical composition and a regular atomic structure. From this basis come all their physical properties. Some of the most obvious physical properties of a mineral are hardness (resistance to scratching), tenacity (resistance to impact), specific gravity (relative density), cleavage (the tendency of some crystals to split along planes of weakest atomic bonding), magnetism, conductivity of electricity, reactibility to acids etc. These measurable physical properties, along with a number of optical ones such as lustre, refractive index and selective absorption of light rays, enable minerals to be positively identified by scientific instruments. The table below is a universally accepted standard of the comparative hardness of minerals. It is called Mohs’ scale, after Frederich Mohs, the mineralogist who devised it. The range is from the softest mineral (talc) to the hardest (diamond). • Talc • Gypsum • Calcite • Fluorite • A
