| Titanite (Sphene) | |
|---|---|
 Titanite crystals onamphibole (image width 2 mm) | |
| General | |
| Category | Nesosilicate |
| Formula | CaTiSiO5 |
| IMA symbol | Ttn[1] |
| Strunz classification | 9.AG.15 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (sameH–M symbol) |
| Space group | P21/a |
| Unit cell | a = 7.057 Å, b = 8.707 Å c = 6.555 Å; β = 113.81°; Z = 4 |
| Identification | |
| Colour | Reddish brown, brown, gray, black, yellow, green, or red, colourless |
| Crystal habit | Flattened wedge-shaped crystals, also massive |
| Twinning | Contact and penetration on {100}, lamellar on {221} |
| Cleavage | Distinct on [110], parting on {221} |
| Fracture | Sub-conchoidal |
| Mohs scale hardness | 5–5.5 |
| Luster | Sub-adamantine tending to slightly resinous |
| Streak | Reddish white |
| Diaphaneity | Translucent to transparent |
| Specific gravity | 3.48–3.60 |
| Optical properties | Biaxial (+); very highrelief |
| Refractive index | nα = 1.843–1.950 nβ = 1.870–2.034 nγ = 1.943–2.110 |
| Birefringence | δ = 0.100–0.160 |
| Pleochroism | Strong: X = nearly colorless; Y = yellow to green; Z = red to yellow-orange |
| 2V angle | 17–40° (measured) |
| Dispersion | r > v strong |
| Other characteristics |  Radioactive – may be metamict |
| References | [2][3][4][5] |
Titanite, orsphene (from Ancient Greek σφηνώ (sphēnṓ) 'wedge'),[5] is a calcium titaniumnesosilicatemineral,CaTiSiO5. Trace impurities ofiron andaluminium are typically present. Also commonly present arerare earth metals includingcerium andyttrium; calcium may be partly replaced bythorium.[6]
TheInternational Mineralogical Association Commission on New Minerals and Mineral Names (CNMMN) adopted the name titanite and "discredited" the name sphene[7] as of 1982,[8] although commonly papers and books initially identify the mineral using both names.[9][10] Sphene was the most commonly used name until the IMA decision, although both were well known.[5] Some authorities[11] think it is less confusing as the word is used to describe any chemical or crystal withoxidized titanium such as therare earth titanatepyrochlores series[12] and many of the minerals with theperovskite structure.[13] 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.[11] Sphene persists as the informal name for titanitegemstones.
Titanite, which is named for its titanium content, occurs as translucent to transparent, reddish brown, gray, yellow, green, or redmonocliniccrystals. These crystals are typicallysphenoid inhabit and are often twinned. Possessing a subadamantine tending to slightly resinousluster, titanite has ahardness of 5.5 and a weakcleavage. Itsspecific gravity varies between 3.52 and 3.54. Titanite'srefractive index is 1.885–1.990 to 1.915–2.050 with a strongbirefringence 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 strongtrichroism, the three colours presented being dependent on body colour. Owing to thequenching effect of iron, sphene exhibits nofluorescence under ultraviolet light. Some titanite has been found to bemetamict, in consequence of structural damage due to radioactive decomposition of the often significant thorium content. When viewed inthin section with apetrographic microscope,pleochroic halos can be observed in minerals surrounding a titanite crystal.
Titanite occurs as a common accessory mineral in intermediate andfelsicigneous rocks and associatedpegmatites. It also occurs inmetamorphic rocks such asgneiss andschists andskarns.[2] Source localities include: Pakistan; Italy; Russia; China; Brazil;Tujetsch,St. Gothard, Switzerland;[5]Madagascar;Tyrol, Austria;Renfrew County, Ontario, Canada;Sanford,Maine,Gouverneur,Diana,Rossie,Fine,Pitcairn,Brewster,New York[5] andCalifornia in the US.
Titanite is a source oftitanium dioxide, TiO2, used inpigments.
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 exceptionaldispersive power (0.051, B to G interval) which exceeds that ofdiamond.[14] 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.
Titanite is commonly mentioned in the Dark Souls video game series as a material used to upgrade weapons and various other items.
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