Titanite_from_Capelinha,_thumb|300pxTitanite or sphene is a
calcium titaniumnesosilicate mineral, CaTiSiO5. Trace impurities of ironand aluminiumare invariably present. Also commonly present are rare earth metals including ceriumand yttrium.
The use of sphene as this mineral's name has been discredited by the
International Mineralogical AssociationCommission on New Minerals and Mineral Names (CNMMN); titanite is the approved name (see [http://www.geo.vu.nl/users/ima-cnmmn/IMA-list.pdf CNMMN report] , p. 134). Sphene was the most commonly used name until the IMA decision, and is less confusing as titanatesare a class of compound with the general formula XTiO3. The name sphene continues to be publishable in peer-reviewed scientific literature, e.g. a paper by Watson et al. was published in early 2008 in the journal Cotributions to Mineralogy and Petrology. Sphene persists as the informal name for titanite gemstones.
Titanite, which is named for its titanium content, occurs as translucent to transparent, reddish brown, gray, yellow, green, or red
monoclinic crystals. These crystals are typically sphenoid(from the Greek "sphenos", meaning wedge) in habit and are often twinned. Possessing a subadamantine tending to slightly resinous lustre, titanite has a hardness of 5.5 and a weak cleavage. Its specific gravityvaries between 3.52 and 3.54. Titanite's refractive indexis 1.885-1.990 to 1.915-2.050 with a strong birefringenceof 0.105 to 0.135 (biaxial positive). Transparent specimens are noted for their strong trichroism, the three colours presented being dependent on body colour. Owing to the quenching effect of iron, sphene exhibits no fluorescenceunder UV. Some titanite has been found to be metamict.
Titanite is a source of
titanium dioxide, TiO2, used in pigments and is admired as a gemstone when suitably free of flaws.
Titanite occurs in
metamorphic rocks such as gneissand schists and also in granular limestones and granite. Source localites include: Pakistan, Italy, Russia, China, Brazil, Switzerland, Madagascar, the Tyrol( Austria), Canada( Renfrew County, Ontario) and the USA ( California).
Use as a gemstone
As a gemstone, sphene is usually some shade of chartreuse and is highly prized for its exceptional dispersive power (0.051, B to G interval) which exceeds that of
diamond. Unfortunately, brittleness and low hardness precludes appropriate use as a ring stone: sphene is more suited to pendants or brooches, or left unset as a collector's stone.
List of minerals
* [http://webmineral.com/data/Titanite.shtml Webmineral data]
* [http://www.mindat.org/min-4977.html Mindat.org]
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