—tourmalinic /toor'meuh lin"ik/, adj./toor"meuh lin, -leen'/, n.any of a group of silicate minerals of complex composition, containing boron, aluminum, etc., usually black but having various colored, transparent varieties used as gems.Also, tourmalin /toor"meuh lin/, turmaline.[1750-60; earlier tourmalin < G Turmalin, ult. < Sinhalese toramalliya carnelian; see -IN2]
* * *Complex silicate mineral that is often used as a gemstone.Three types of tourmaline, distinguished by the presence of certain elements, are usually recognized: iron tourmaline (schorl) is black, magnesium tourmaline (dravite) is brown, and alkali tourmalines may be pink, green, blue, or colourless. Tourmaline is most common in granite pegmatites. Gem-quality stones are found especially in the U.S., Brazil, Russia, and Madagascar.
* * *▪ mineralborosilicate mineral of complex and variable composition. Three types of tourmaline, distinguished by the predominance of certain elements, are usually recognized: iron tourmaline (schorl), black in colour; magnesium tourmaline (dravite), brown; and alkali tourmaline, which may be pink (rubellite), green (Brazilian emerald), or colourless (achroite). Some crystals are pink at one end and green at the other; concentric colour zoning may also occur. The coloured varieties, when transparent and free from flaws, are cut as gems.Tourmaline is very abundant and has the best-developed crystals in pegmatites and in metamorphosed limestones in contact with granitic magmas. Because tourmaline is resistant to weathering, it accumulates in detrital deposits and is a common accessory mineral in sedimentary rocks. Gem-quality pegmatites are found in the United States (southern California and Maine), Brazil, and Madagascar.In addition to its use as a gem, tourmaline is employed in pressure devices because of its piezoelectric properties—i.e., its ability to generate electric charge under mechanical stress or its change in shape when voltage is applied. It has been used in depth-sounding apparatus and other devices that detect and measure variations in pressure.Coloured crystals of tourmaline are very strongly dichroic—i.e., they are of different colour when viewed in the direction of different axes; the ordinary ray is almost completely absorbed. Plates cut parallel to the vertical axis of a tourmaline crystal allow only the extraordinary ray through; if two such plates are placed in crossed position, the light is entirely blocked. A pair of these plates form a very simple polarizing apparatus known as tourmaline tongs.
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Tourmaline — Schorl Tourmaline General Category Cyclosilicate Chemical formula (Ca,K,Na,[ … Wikipedia
Tourmaline — Catégorie IX : silicates Tourmaline Brésil Général … Wikipédia en Français
TOURMALINE — Cyclosilicate cristallisant dans le système rhomboédrique. Du mot cinghalais touramali , la tourmaline se présente sous forme de cristaux prismatiques allongés parallèlement à l’axe ternaire. Les plus courants sont de petite taille, mais ils… … Encyclopédie Universelle
Tourmaline — Tour ma*line, n. [F. tourmaline, cf. It. turmalina, tormalina, NL. turmalina, turmalinus; all fr. tournamal, a name given to this stone in Ceylon.] (Min.) A mineral occurring usually in three sided or six sided prisms terminated by rhombohedral… … The Collaborative International Dictionary of English
tourmaline — complete silicate of aluminum and boron, 1759, ultimately from Sinhalese toramalli, a general name for cornelian … Etymology dictionary
tourmaline — [toor′mə lin, toor′məlēn΄] n. [Fr, ult. < Sinhalese tōramalli, carnelian] a very hard, piezoelectric, rhombohedral mineral, (Na,Ca)(Mg,Fe,Al,Li) 3Al6 (BO3) 3 (Si6O18)(OH) 4, of various colors, used as a gem and in making pressure gauges … English World dictionary
tourmaline — turmalinas statusas T sritis fizika atitikmenys: angl. tourmaline vok. Turmalin, m rus. турмалин, m pranc. tourmaline, f … Fizikos terminų žodynas
tourmaline — (tour ma li n ) s. f. Minéral siliceux, de composition très complexe, qui jouit de la propriété de prendre la bipolarité lorsque les extrémités de ses cristaux sont inégalement chauffées. • Toutes les tourmalines sont à demi transparentes ; les … Dictionnaire de la Langue Française d'Émile Littré
tourmaline — turmalinas statusas T sritis chemija apibrėžtis Mineralas. formulė NaFe₃Al₆[(OH)₄|(BO₃)₃|Si₆O₁₈] atitikmenys: angl. tourmaline rus. турмалин … Chemijos terminų aiškinamasis žodynas
tourmaline — noun Etymology: Sinhalese toramalli carnelian Date: 1759 a mineral of variable color that consists of a complex borosilicate and is valued as a gem when transparent and cut … New Collegiate Dictionary