The word iolite was derived from the Greek "ios" meaning violet and "lithos" meaning stone. Cordierite was named after the Frech geogist who studied the stone, Mr Cordier. Iolite is actually a very attractive gem. It refractive index is in the 1.5 to 1.60 range. The pleasant color and strong pleochroism makes up for its lower luster. Clean stones of over 10 carat sizes are rare. Deep purple colors maybe found in Sri Lanka and Myanmar. Cat's eye variety has also been reported.
The chemical formula is (Mg,Fe)2 Al4Si5O18 Hardness is 7 - 7.5 Luster is vitreous. Density is 2.53 to 2.61. Cleavage is one direction. Fracture is conchoidal. Brittle. Pleochroisn is distinct and instense. Sources include Sri Lanka, Myanmar, Madgascar, USA, Brazil,India, Tanzania, Namibia |