Quarterly Crystal: Ferrocolumbite in Topaz
The author recently acquired a 239.25 ct transparent well-formed topaz crystal from the collection of Leon M. Agee. The crystal from the Shigar Valley in Pakistan, shown in figure 1, has a flat base formed by a cleavage plane. The termination appears to be a pyramid form. The crystal plays host to two prominent opaque black inclusions and one smaller similar-appearing inclusion that is close to the surface of the host (figure 2). The two larger inclusions were too deep in the topaz to analyze. However, the small inclusion was near the surface of one of the prism faces and could be reached by laser Raman microspectrometry. Testing showed a very close match to ferrocolumbite (columbite-Fe). Because of the resemblance between the smaller inclusion and the two larger ones, we concluded that the two larger inclusions were also ferrocolumbite. As an interesting aside, these inclusions are reminiscent of star cruisers in the Star Wars anthology.
