Micro-World Gems & Gemology, Spring 2023, Vol. 59, No. 1

Inclusions in Chondrodite

Kendra Carty and Amy Cooper

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Figure 1. This 4.63 ct chondrodite contained irregular multiphase and reflective iridescent platelets with a bright orangy yellow color. Photo by Adriana Gudino; courtesy of Bill Vance.
 
Figure 1. This 4.63 ct chondrodite contained irregular multiphase and reflective iridescent platelets with a bright orangy yellow color. Photo by Adriana Gudino; courtesy of Bill Vance.

The authors recently examined a 4.63 ct orangy yellow pear modified brilliant (figure 1). The gemological properties as well as infrared and Raman spectroscopy identified the stone as chondrodite.

Figure 2. Platy inclusions were observed throughout the chondrodite. Photomicrograph by Nathan Renfro; field of view 4.11 mm.
 
Figure 2. Platy inclusions were observed throughout the chondrodite. Photomicrograph by Nathan Renfro; field of view 4.11 mm.

Microscopic observation revealed a lively inclusion scene with colorless reflective and iridescent platy inclusions (figure 2). Dark, highly reflective platelets of graphite, which can be associated with low-relief colorless crystals of various minerals (figure 3), were also confirmed by Raman analysis.

Figure 3. Dark, highly reflective platelets of graphite as well as unidentified low-relief colorless inclusions of multiple minerals were also observed in the chondrodite. Photomicrograph by Nathan Renfro; field of view 0.91 mm.
 
Figure 3. Dark, highly reflective platelets of graphite as well as unidentified low-relief colorless inclusions of multiple minerals were also observed in the chondrodite. Photomicrograph by Nathan Renfro; field of view 0.91 mm.

Chondrodite, Mg5(SiO4)2(F,OH)2 is a member of the humite group. This rare mineral occurs primarily in metamorphosed limestones and dolomites (W.L. Roberts et al., Encyclopedia of Minerals, 2nd ed., Van Nostrand Reinhold, New York, 1990, p. 170). If contact metamorphism occurs in an area with sufficient magnesium, chondrodite and other associated magnesium-bearing minerals such as spinel, phlogopite, and tremolite may form.

Chondrodite has been found to originate from Tanzanian localities at Mahenge (Winter 2011 Gem News International, p. 316), Sumbawanga (Winter 2007 Gem News International, pp. 377–379), and Tanga (B. Clark, “Chondrodite reportedly from Tanga, Tanzania,” Journal of Gemmology, Vol. 34, No. 8, p. 655). It has also been identified as an inclusion in a spinel from Mogok, Myanmar (Winter 2021 G&G Micro-World, p. 383). The gemological properties of this stone were consistent with material from Mahenge, but the origin could not be confirmed.

Chondrodite is an uncommon mineral and even more rare as a gemstone. This exceptional example of a bright orangy yellow color, faceted by Bill Vance of Vance Gems, showcases the types of inclusions that can be found in this gemstone.

Kendra Carty is a staff gemologist, and Amy Cooper is a senior staff gemologist, at GIA in Carlsbad, California.