Rutile: Gemstone Information
Rutile with anatase and brookite is a trimorph of TiO2 in the rutile group and forms characteristic slender prismatic striated lengthways, variably terminated and often geniculate twinned crystals of the tetragonal system with a metallic to adamantine lustre and most frequently pale brown to yellow. The hardness is 6–6.5 and the SG 4.23. The RI for the ordinary and extraordinary rays is 2.605–2.613 and 2.899–2.901, uniaxial positive with birefringence 0.287 and dispersion, very notable in synthetic transparent faceted stones, 0.280. Rutile occurs as a common high-temperature, high pressure accessory mineral in igneous rocks and granite pegmatites and in regionally metamorphosed rocks including crystalline limestones. Rutile needles are common inclusions in a number of gem minerals but fine unenclosed crystals are found at a number of Swiss locations. Larger crystals are found at Conquista and Ibitiara, Bahia, Brazil.