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In addition, it must be hard and durable. Its value increases if it is also rare.The beauty of a gem is measured in terms of its clarity, brilliance, and color. Comments
Silicatesâincluding quartz, mica, olivine, and precious minerals such as emeraldsâare the most common class of minerals, as well as the major components of most rocks. Oxides, sulfides, sulfates, carbonates, and halides are other major mineral classes.Gemstones. Many minerals form beautiful crystals, but the most prized of all are gemstones. Uncut gems are often fairly ordinary looking.It's only when they are cut and polished that they obtain the brilliance and luster that makes them so valued.Historically gems have been divided into precious and semiprecious classes.inerals and gems are classified by their physical properties, including hardness, luster, color, density, and magnetism. They're also identified by the ways in which they break, or the type of mark, or streak, that they leave when rubbed on a laboratory tool called a streak plate. More Â».