The mineral Titanite is a compound that finds use across a range of applications. It is sometimes referred to by its older name, Sphene, which is derived from the Greek word for “wedge” due to the characteristic shape of its crystals. This accessory mineral is valued for two distinct physical properties: a moderate hardness of 5 to 5.5 on the Mohs scale and an exceptionally high optical dispersion.
Titanite’s Value in Jewelry
Titanite is highly prized in the world of gemstones for its remarkable optical characteristics, which give it a spectacular brilliance and fire. The mineral possesses one of the highest dispersions of any known gemstone, measuring 0.051, which actually exceeds the light-splitting ability of a diamond (0.044). This high dispersion results in intense flashes of multicolored light often referred to as “fire.” The mineral also exhibits a very high refractive index, ranging from 1.843 to 2.110, which contributes to its strong luster.
The colors of gem-quality titanite typically range from a rich golden-yellow and warm brown to a vibrant yellowish-green or pure green. This palette, combined with its strong pleochroism—the ability to show different colors when viewed from different angles—makes it a captivating stone for collectors. However, its relatively moderate hardness of 5 to 5.5 on the Mohs scale means it is softer than many other popular jewelry stones, such as quartz or sapphire. Consequently, titanite jewelry requires careful handling and is often set in protective mountings to prevent scratching or abrasion.
Source Material for Titanium Dioxide
The most significant industrial use of Titanite lies in its capacity as a titanium-bearing mineral, which can be processed to yield titanium dioxide (\(\text{TiO}_2\)). While the primary commercial sources for titanium dioxide production are the minerals Ilmenite and Rutile, Titanite remains a viable, albeit secondary, feedstock. The titanium component is separated from the calcium and silicon and then purified into the oxide form.
The resulting titanium dioxide is overwhelmingly used as a brilliant white pigment, often called titanium white or Pigment White 6, due to its unparalleled opacity and brightness. This pigment is incorporated into a vast array of consumer and industrial products, where it provides high reflectivity and coverage:
- Paints
- Coatings
- Plastics
- Paper
In a secondary application, the titanium derived from titanite and other ores can be utilized in the production of ferro-titanium alloys. This ferroalloy, composed of iron and 45–75% titanium, is added to steelmaking to act as a cleansing agent that removes impurities like oxygen and nitrogen. It also contributes to a finer grain structure in the final metal product.
Measuring Geological Time
Beyond its aesthetic and industrial applications, Titanite holds a powerful function as a specialized tool in the field of geochronology, which is the science of determining the age of rocks and geological events. The mineral’s crystal structure is highly effective at incorporating uranium (\(\text{U}\)) into its lattice when it forms, while simultaneously excluding lead (\(\text{Pb}\)), the stable end product of uranium’s radioactive decay chain. This makes it an excellent mineral for \(\text{U-Pb}\) dating, which calculates the time elapsed since the mineral crystallized.
Titanite is particularly useful for dating metamorphic events and tracking the thermal history of rocks because its \(\text{U-Pb}\) system has a relatively low closure temperature, typically ranging from about \(550\) to \(650^\circ \text{C}\). The closure temperature is the point below which the lead atoms cease to diffuse out of the crystal structure, effectively “setting the clock” for the mineral’s age determination. If a rock is reheated above this temperature, the titanite’s \(\text{U-Pb}\) clock is reset, and the measured age will record the time of the metamorphic event or the subsequent cooling. By combining titanite dates with those from other minerals that have higher closure temperatures, geologists can construct a detailed timeline of a rock’s entire geological history.