Corundum – Ruby

Description:

Ruby is a variety of the mineral species corundum (ko-RUN-dum); hexagonal (trigonal) crystal system.
Major Sources: Thailand, Burma, Kampuchea, Sri Lanka, Kenya.

Appearance:

• transparent to opaque
• orangy red to purplish red, brownish red
• phenomena: asterism, chatoyancy (very rare)

Identification:

Optic Character: DR, uniaxial negative
Refractive Index: 1.762-1.770 (+.009, -.005) 
Absorption Spectra: a strong doublet at 694.2 and 692.8 nm which may appear as a fluorescent line, fairly distinct lines at 668 and 659.2 nm, broad absorption from 620 to 540 nm, a strong doublet at 476.5 and 475 nm, a weak line at 468.5 nm, and general absorption of the violet
Cause of Color: chromium, with possible modification of color by iron and titanium
Specific Gravity: 4.00 (+-.05) 
Hardness: 9 ; Toughness: excellent, except in repeatedly twinned or fractured stones

Stone Information from:

Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6
Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6
Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1
https://www.gemdat.org/gem-3473.html
https://www.mindat.org/min-3473.html