Natural Black Rutile Faceted Pear Drops Briolette Length is 4.5 inches and Size 8 to 17mm approx. Rutile has among the highest refractive indices of any known mineral and also exhibits high dispersion. Natural rutile may contain up to 10% iron and significant amounts of niobium and tantalum.Rutile derives its name from the Latin rutilus, red, in reference to the deep red color observed in some specimens when viewed by transmitted light.