Gem of the Month

Each month this section will feature either a topic of interest to gem lovers or one special gemstone with background on the material and its value.

Sphene, also known as "titanite" (due to its titanium content), is a yellow, orange, brown or green gem with many gradations between those colors. The usual colors are created by iron and rare-earth element impurities. Sphene is found primarily in Madagascar, Mexico, Canada and, historically, Austria. Although reasonably available in the marketplace, it is virtually unknown to the general public.

Several gemological characteristics make it beautiful and desirable as a collector's stone or, with care, for jewelry use. Its dispersion ("fire") is one of the highest of all gem materials and is higher than diamond (although damnably hard to capture in a photo). The body color, degree of inclusions, cutting orientation and cutting style may enhance or obscure this feature. If well polished, the luster can approach or equal that of diamond, but the gem is difficult to polish well. The high birefringence usually makes some doubling of facet images visible within the stone giving it a degree of internal "fuzziness" similar to that often seen in zircon or peridot. A rare variety termed chrome sphene is colored by chromium and is an intense green.

Enhancements, imitations or synthetics are not known, but the natural gem sphalerite which also shows strong dispersion and comes in the same colors might be confused with it. Sphalerite is too delicate to be used for jewelry, though and is rarely seen outside the collector market.

This gem is somewhat risky as a jewelry stone due to its softness and brittleness, but beautiful if set protectively and worn occasionally. Shield this gem from knocks, heat and exposure to acids; do not clean with steam or ultrasonics, and it will be a spectacular addition to your gemstone collection or jewelry case.

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Value

As is so common in gemstones, color, clarity and size are the most important value factors, followed by the skill and artistry shown in cutting. A preference exists for stones that are lighter in tone, especially yellows and light oranges and greens which are able to best exhibit this gem's magnificent dispersion. Size is definitely a premium characteristic with this species. Chrome sphene is the most valuable type. In general, specimens with reasonably good clarity (this stone is rarely even eye clean), strong and attractive body color, and showing at least some dispersion command the best prices.

Gemological Data:

Makeup: Calcium titanium silicate

Hardness: 5-5.5

Crystal structure: monoclinic

Cleavage: weak, in two directions

Density: 3.53

RI: 1.90-2.03

Birefringence: .120

Dispersion: .051

Luster: sub-adamantine to adamantine

Pleochroism: strong: yellow-green, orange, near colorless