Titanite
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Titanite, or sphene (Template:Etymology),<ref name="Dana"/> is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly replaced by thorium.<ref>Template:Cite book</ref>
NomenclatureEdit
The International Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN) adopted the name titanite and "discredited" the name sphene<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> as of 1982,<ref>Template:Cite journal</ref> although commonly papers and books initially identify the mineral using both names.<ref>Template:Cite book</ref><ref>Template:Cite book</ref> Sphene was the most commonly used name until the IMA decision, although both were well known.<ref name="Dana"/> Some authorities<ref name="Hayden">Template:Cite journal</ref> think it is less confusing as the word is used to describe any chemical or crystal with oxidized titanium such as the rare earth titanate pyrochlores series<ref>Template:Cite journal</ref> and many of the minerals with the perovskite structure.<ref>Template:Cite journal</ref> The name sphene continues to be publishable in peer-reviewed scientific literature, e.g. a paper by Hayden et al. was published in early 2008 in the journal Contributions to Mineralogy and Petrology.<ref name="Hayden"/> Sphene persists as the informal name for titanite gemstones.
Physical propertiesEdit
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 in habit and are often twinned. Possessing a subadamantine tending to slightly resinous luster, titanite has a hardness of 5.5 and a weak cleavage. Its specific gravity varies between 3.52 and 3.54. Titanite's refractive index is 1.885–1.990 to 1.915–2.050 with a strong birefringence of 0.105 to 0.135 (biaxial positive); under the microscope this leads to a distinctive high relief which combined with the common yellow-brown colour and lozenge-shape cross-section makes the mineral easy to identify. 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 fluorescence under ultraviolet light. Some titanite has been found to be metamict, in consequence of structural damage due to radioactive decomposition of the often significant thorium content. When viewed in thin section with a petrographic microscope, pleochroic halos can be observed in minerals surrounding a titanite crystal.
OccurrenceEdit
Titanite occurs as a common accessory mineral in intermediate and felsic igneous rocks and associated pegmatites. It also occurs in metamorphic rocks such as gneiss and schists and skarns.<ref name=Handbook/> Source localities include: Pakistan; Italy; Russia; China; Brazil; Tujetsch, St. Gothard, Switzerland;<ref name="Dana"/> Madagascar; Tyrol, Austria; Renfrew County, Ontario, Canada; Sanford, Maine, Gouverneur, Diana, Rossie, Fine, Pitcairn, Brewster, New York<ref name="Dana"/> and California in the US.
UsesEdit
Titanite is a source of titanium dioxide, TiO2, used in pigments.
As a gemstone, titanite is usually some shade of chartreuse, but can be brown or black. Hue depends on iron (Fe) content, with low Fe content causing green and yellow colours, and high Fe content causing brown or black hues. Zoning is typical in titanite. It is prized for its exceptional dispersive power (0.051, B to G interval) which exceeds that of diamond.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Jewelry use of titanite is limited, both because the stone is uncommon in gem quality and is relatively soft.
Titanite can also be used as a U-Pb geochronometer, specifically in metamorphic terranes.
In popular cultureEdit
Titanite is commonly mentioned in the Dark Souls video game series as a material used to upgrade weapons and various other items.
Image galleryEdit
- Titanit.jpg
Specimen from the mineral collection of the Naturmuseum Senckenberg in Frankfurt am Main
- Titanite-tt56a.jpg
Titanite crystal that is totally gemmy and transparent, with a light olive-green color, perched on matrix of calcite and epidote
- Titanite-Adularia-Clinochlore-275128.jpg
Bright green, twinned crystal of titanite with adularia and minor clinochlore on matrix
- Titanite-163984.jpg
Olive-green titanite spear point set in matrix from Pakistan
- Titanite-37979.jpg
Green titanite crystal perched right at the top of a column of gray, chlorite-included crystals
- Titanite-23006.jpg
Yellow-green titanite twinned crystal perched vertically on the matrix