We noticed transparent crystals cut through on the surface of this ruby from Mozambique’s Montepuez region. Micro Raman revealed the lower luster crystal to be pargasite (amphibole), while the two higher relief crystals tested as spinel. Because their luster is even higher the surrounding ruby, their refractive index is above 1.77. This suggests that rather than being pure spinel (MgAl2O4), they are probably mixed with another species, such as chromite (Fe2+Cr3+2O4). Chromite has an RI of 2.08 to 2.16.
Natural Ruby • Mozambique • Enhancements: None Detected (None) • Lighting Conditions: Dark Field + Diffuse Overhead Fiber Optic
Photographer: Richard W. Hughes •
Image Number: A-003-6687-1 • Field of View = 2 mm • Date Posted: 24 July 2020
Hughes, R.W., Manorotkul, W. and Hughes, E.B. (2017) Ruby & Sapphire: A Gemologist's Guide. Bangkok, Lotus Publishing, 816 pp.; RWHL*.