Octahedron-shaped inclusions are the most common feature of spinels from all sources. In some cases they may actually be solid crystals of spinel. In other cases, such as this fingerprint with tiny rows of octahedra, they represent tiny negative crystals. This example is in a stone from Mahenge, Tanzania. In certain cases, these negative crystals may be filled with a foreign substance (such as white dolomite, yellow phlogopite or black hercynite spinel).
Natural Spinel • Tanzania; Mahenge • Enhancements: None Detected (None) • Lighting Conditions: Diffuse Light Field (Transmitted Light)
Photographer: E. Billie Hughes •
Image Number: A-001-3432-1 • Date Posted: 01 December 2015
Gübelin, E.J. and Koivula, J.I. (2005) Photoatlas of Inclusions in Gemstones, Volume 2. Basel, Switzerland, Opinio Publishers, 830 pp.; RWHL*.