Semi-Precious Gemstones: Titanite (Sphene)
Sphene used in Jewelry
Source: Austria, Brazil, Canada, China, Germany, Italy, Madagascar, Norway, Pakistan, Russia, Sri Lanka, Switzerland, USA
Titanite is a nesosilicate mineral that derives its name from its titanium content, making titanite a potential source of titanium dioxide used in paint pigments. As a cut gemstone, titanite is commonly known as "sphene" (sphen) which is the Greek word (sphenoid) for "wedge," referring to its lamellar, wedge-shaped crystal habit.
The mineral titanite (titanit German, titanita Spanish) is a calcium titanium nesosilicate is a minor gemstone that is a common constituent in magmatic (igneous), metamorphic and hydrothermal rock, and is an accessory mineral found within granite, diorite, granodiorite and syenite. Larger, transparent titanite crystals can be found in chlorite schists, gneisses, and marble. Titanite can also found as detritus within sedimentary deposits.
Rough, wedge-shaped titanite crystal |
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Faceted sphene (photo: © AfricaGems.com) |
The mineral is associated with amesite, apatite, feldspar, iron ore, pyroxene, quartz and zircon, as well as the rare earth metals cerium and yttrium. Titanite can be mildly radioactive, with levels greater than 70 Bq/gram. As a consequence of structural damage due to radioactive decomposition, titanite can be completely metamict, and when observed under microscope, pleochroic halos can be seen in the minerals that surround an intact sphene crystal.
Optical Characteristics of Titanite
Titanite can have very high light dispersion (0.051, B to G interval) which can exceed the brilliance, or "fire" of in diamond when it is brilliant cut (faceted). It also exhibits high birefringence, it will appear as a high-order white under crossed nicols prisms, or an equivalent polarizing device. Sphene can also exhibit strong trichroism on three axes, the x-axis: colorless, greenish-yellow (chartreuse) or yellowish-brown; y-axis: greenish-yellow, yellowish-brown, or yellowish-green; and the z-axis: pink, reddish-orange or yellow. Heating can increase the amount of orange or reddish hues in the stone.
Sphene (Titanite) Crystallography, Chemistry, Physical Properties
Sphene (Titanite) Optical Properties
Titanite forms elongated and flattened (wedge-shaped) crystals which are typically twinned, but can also form with a compact, lamellar or massive crystal habit, with fine-grained, distinctly foliated crystals. Titanite can be easily recognized by its sphenoidal (wedge) shape as seen in a thin section.
Sphene can be faceted but due to its brittleness and lack of hardness, sphene is best used in safer gemstone settings such as brooches or pendants. Other mineral varieties of titanite are eucolite-titanite, greenovite, grothite, keilhauite, stanniferous titanite and yttrian titanite. Synonyms for titanite are aspidelite, castellite, lederite and ligurite.
Bibliography and Reference on Titanite (Sphene)
1. Paul R. Shaffer, Rocks, Gems and Minerals  . Martin's Press
2. D. Papineau, T. Yesavage, Crystal structure of Titanite (Sphene) . www.colorado.edu
3. Renee Newman, Gemstone Buying Guide . International Jewelry Publications; 2nd edition
4. Antoinette L . Matlins, Antonio C. Bonanno, Gem Identification Made Easy . Gemstone Press
5. Africa Gems, Cut Sphene . www.africagems.com
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