Absorption Spectrum The ferric iron spectrum dominates these stones. In green and blue-green gems, rich in iron, there are lines at 4710, 4600, and 4500 in the blue-green region. Also lines at 4500 and 4600 may seem to merge and become a broad band. The three bands described are generally known as the 4500 complex and are very distinctive in sapphires. Some blue Sri Lanka sapphires also show a 6935 red fluorescent line, and the 4500 line is very weak in these gems. Synthetic color change sapphires show a line 4740. See main Sapphire gem listing for more information.
Colors Usually, blue, bluish purple, and violet-purple. More rarely, green, yellow, and pink.
Crystallography Hexagonal (trigonal). Crystals common, often barrel-shaped, prisms with flat ends, sometimes bipyramidal; also massive, granular, in rolled pebbles.
Fracture Conchoidal; frequent parting
Luminescence Natural color change sapphires: inert to strong red in LW, inert to moderate red to orange in SW. Synthetic color change sapphires: moderate orange to red in LW and SW, may fluoresce red in LW and mottled blue in SW.
Luminescence Type Fluorescent, UV-Long, UV-Short, X-ray Colors
Luster Vitreous to adamantine.
Optics RI: o = 1.757-1.770; e = 1.765-1.779 (usually 1.760, 1.768); Uniaxial (-).
Phenomena Asterism, color change, chatoyancy.
Pleochroism Very pronounced. See main Sapphire gem listing.
Polish Luster Vitreous to subadamantine.
Refractive Index 1.757-1.779
Specific Gravity 3.99-4.10; usually near 4.0.
Transparency Transparent to opaque.
