COLOR TYPES FOR SPHENE
A brief discribtion of the color type for Sphene used at Agl Thai Laboratory Gemology.
Titanite, or sphene (comes from the Greek word “sphenos,” meaning wedge, a reference to the mineral’s characteristic wedge-shaped crystals), is a calcium titanium nesosilicate mineral, CaTiSiO5. Trace impurities of iron and aluminium are typically present.
Sphene persists as the informal name for titanite gemstones, for its exceptional dispersion, resulting in gemstones that show brilliant fire.
Sphene has a hardness of 5 to 5.5 and a distinct in to directions cleavage. Its specific gravity varies between 3.52 (+ - .20). Sphene refractive index is 1.900 –2.110 with a strong birefringence of 0.105 to 0.135 (biaxial positive); Its high birefringence often results in visible doubling of facets within the stone. under the microscope this leads to a distinctive high relief which combined with the common yellow-brown color and lozenge-shape cross-section makes the mineral easy to identify.
It’s also pleochroic, showing more than one color depending on the angle from which you view it; sphene’s transparent specimens are notable for their trichroism, showing three different colors.
Sphene’s color range is yellowish brownish Green, greenish-yellow, yellow-brown, brownish Orange and Brown or sometimes gray or nearly black. There are also pinks and reds, which are rarer, as well as some black and colorless material.
Chrome sphene is the most valuable type.