Barite (#48)

USA Cerro Warihuyn, Miraflores Huamalias, Huanuco Province, Peru

 

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Barite, sometimes spelled baryte, is a barium sulfate, BaSO •. It is a rather common mineral found in several geologic environments. It can originate from hydrothermal processes (such as in lead-zinc ore deposits), from evaporation, and from biogenic activity. It is the major source of barium, but has other important uses. It is quite dense (4.5 g/cm3), which leads to its principal use in drilling muds, to counteract high pressures in the rocks at great depth. It is also used as an additive in paints and in medical applications.

These colorless crystals are not typical of all barite, which may be white, yellow (golden), brown, gray, or blue. The color can sometimes be caused by physical impurities incorporated during crystal growth from the surrounding environment, but is most often caused by color centers. Color centers are not stable with heat and radiation. For example, golden barite may be made colorless by heating, and then turned pale blue by irradiation of the same specimen with X-rays.

Barite is the "principal mineral" in the barite group. That group consists of barite and three other minerals that have the same crystal structure. They are celestine (SrSO.), anglesite (PbSO.), and hashemite (Ba(Cr,S)O•). In celestine and anglesite, strontium and lead, respectively, replace barium in the crystal structure. In hashemite, chromium substitutes for some of the sulfu r. These four minerals are said to be isomorphous (literally, same form). There are many isomorphous groups in mineralogy. Mother Nature finds arrangements of atoms that work well and repeats them with different chemical elements. The substitutions work because the atoms involved have similar sizes and, usually, the same charges. If the substituent atoms are too different in size, a different structure that is more stable forms.