Rai-Iz Ophiolite Massif, Yamalo-Nenets Autonomous Okrug, Russia
Rai-Iz ultramafic massif, part of the Lower Paleozoic Khodatin-Voikar-Syn'insky ophiolite belt.Lenses of ruby-bearing anorthosites are found at the southern termination of the massif in fine- to medium-grained dunites with lenses of metasomatic, giant-grained dunite and chromite ore. The lenses have a concentrically zoned internal structure.
Ruby is confined to the micaceous zone in association with phlogopite, chromium-rich spinel and fuchsite. Crystals have tabular or barrel-like shapes. Parting parallel to the pinacoid is characteristic of the large crystals and divides them into 1 to 5 mm plates.
The dark red ruby contains numerous inclusions of chrome-spinel, phlogopite, fuchsite and oligoclase. Gas-liquid inclusions are also present. The refractive indices are 1.735 - 1.778 (Shcherbakova and Suturin, 1990).
Ref: E.Ya. Kievlenko, Geology of gems, 2003, p. 58