Micro-World Gems & Gemology, Fall 2023, Vol. 59, No. 3

Quarterly Crystal: Dravite in Fluorapatite

John I. Koivula, Nathan Renfro, and Maxwell Hain

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Figure 1. Dark yellowish to brownish green needle-like inclusions dominate the interior of this 21.36 ct Portuguese fluorapatite on siderite matrix. Photo by Adriana Robinson.
 
Figure 1. Dark yellowish to brownish green needle-like inclusions dominate the interior of this 21.36 ct Portuguese fluorapatite on siderite matrix. Photo by Adriana Robinson.

Growing from an angular matrix plate of brown siderite, a doubly terminated hexagonal crystal weighing 21.36 ct with a very light purplish blue color (figure 1) was identified as fluorapatite by Raman analysis. As the photo shows, the semitransparent crystal clearly hosts a number of randomly arranged, eye-visible, translucent acicular inclusions. The fluorapatite thumbnail specimen, from the Panasqueira mine in the Castelo Branco district of Covilhã, Portugal, was acquired by author JIK from the collection of Dr. Vasco Trancoso at auction in June 2023. When the specimen was examined microscopically, the acicular morphology and dark yellowish to brownish green bodycolor of the inclusions, as well as their behavior in polarized light, suggested they might be tourmaline. Laser Raman microspectrometry was able to pinpoint their identity as dravite (figure 2), a member of the tourmaline group.

Figure 2. Raman analysis was used to identify the acicular inclusions in the fluorapatite host crystal as dravite tourmaline. Photomicrograph by Nathan Renfro; field of view 7.37 mm.
 
Figure 2. Raman analysis was used to identify the acicular inclusions in the fluorapatite host crystal as dravite tourmaline. Photomicrograph by Nathan Renfro; field of view 7.37 mm.

John Koivula is analytical microscopist, Nathan Renfro is senior manager of colored stone identification, and Maxwell Hain is a staff gemologist, at GIA in Carlsbad, California.