Micro-World
Gems & Gemology, Spring 2017, Vol. 53, No. 1

Astrophyllite in Bastnäsite-(Ce)

John I. Koivula
Bastnäsite from Pakistan
Figure 1. This 6.92 mm bastnäsite-(Ce) from Pakistan contains numerous straight and curving acicular inclusions of astrophyllite. Photo by Kevin Schumacher.

Pakistan’s Zagi Mountains are known as a source for both astrophyllite and bastnäsite-(Ce). The two minerals often grow together, with bastnäsite-(Ce) overgrowing stalks and fibers of astrophyllite; the latter is then sometimes incorporated as inclusions in the bastnäsite-(Ce). We refer to these types of inclusions as “protogenetic.”

The author recently had the opportunity to examine the brownish orange bastnäsite-(Ce) seen in figure 1. The 1.40 ct oval modified brilliant, provided by Luciana Barbosa (Gemological Center, Asheville, North Carolina), hosted an abundance of eye-visible inclusions of astrophyllite (figure 2), both straight and curved, that were identified by Raman analysis. Some of the included fibers and stalks appear to have been partially altered or coated with iron compounds.

Inclusions in bastnäsite
Figure 2. Magnification affords a more detailed view of the bastnäsite-(Ce) inclusions. Photomicrograph by Nathan Renfro; field of view 2.85 mm.

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