Minerals and Metals in Ancient India v2.c47.143

v2.c47.143

There is another variety of Ruby belonging to a different family: *Spinel* Group RᴵᴵRᴵᴵᴵO₄. *Ruby Spinel* is a magnesia alumina spinel MgAl₂O₄. This is clear red on account of some association of chromium in the structure. There may be little iron also. Some varieties are: (a) *Spinel-Ruby*, deep red; (b) *Balas-Ruby*, rose red; (c) *Rubicalle*, yellow or orange red; and (d) *Almandine*, violet, which is different from the almandine in the *Garnet* family. *Ceylonite* is Fe-Mg Spinel, opaque, dark green brown or black. Spinel Rubies are distinguished by their octahedral form, hardness and infusibility. Zircon has a higher specific gravity. True or Oriental Ruby is harder and is distinguished optically. Garnet is softer and fusible.