Tourmaline

Tourmaline is a group of complex boron-bearing silicate minerals with varied chemical compositions, crystal structures, and colors. Some varieties are prized as gemstones.

Silicate minerals: Minerals built from silicon–oxygen tetrahedra, often combined with other elements. Tourmaline belongs to this broad mineral class, whose structural units form its crystal framework.
Tourmaline supergroup: A mineral supergroup comprising tourmaline minerals with related crystal structures and compositions. Its subdivisions show how changing chemical constituents creates distinct tourmaline species.
Gemstone: A mineral or other material cut and polished for ornamental use. Transparent, attractive tourmaline varieties are cut and valued as gemstones.
Erasmus Bartholin: A Danish physician and scientist who described double refraction in Iceland spar in 1669. His optical observations established a context for studying unusual properties in transparent minerals.
Beryl: A beryllium aluminum silicate mineral that includes emerald and aquamarine. Beryl offers a familiar colored-gem comparison but has a different structure and chemistry.
Boron: A chemical element with symbol B and atomic number 5. Boron is a defining constituent of tourmaline’s silicate structures.
Trigonal crystal system: A crystal system characterized by a threefold rotational symmetry axis. Tourmaline’s trigonal symmetry governs its elongated crystals and directional physical properties.
Paraíba tourmaline: A copper-bearing tourmaline prized for vivid blue to green colors. This rare variety exemplifies how trace elements can produce unusually intense gemstone colors.
Johan Gottschalk Wallerius: An eighteenth-century Swedish chemist and mineralogist who systematized mineral classification. His mineralogical work belongs to the period when European scholars began classifying tourmaline specimens.
Topaz: An aluminum silicate fluoride mineral used as a gemstone. Topaz can resemble tourmaline in color while differing in composition and crystal structure.

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