Formula: Al2(SiO4)(F,OH)2
Colour: Colourless, white, pale blue, light green, yellow, yellowish brown, or red
Lustre: Vitreous
Hardness:   8
Specific Gravity: 3.4 - 3.6
Crystal System: Orthorhombic
Name: Named after Topasos Island in the Red Sea. In antique times, the name was probably used for the gemstone that is now known as Peridot.