Gem News International Gems & Gemology, Winter 2013, Vol. 49, No. 4

Scheelite and Hübnerite Inclusions in Quartz from China

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Figure 1. Quartz with scheelite and hübnerite inclusions from China, 2.3 cm wide, in daylight (left) and under short-wave UV light (right). Photos by Jaroslav Hyršl.
Scheelite, a very popular mineral among collectors, is very rarely found as an inclusion in quartz (J. Hyršl and G. Niedermayr, Magic World: Inclusions in Quartz, Bode Verlag, Haltern, Germany, 2003, p. 147). One such quartz specimen, measuring 4.5 cm high and with very high luster (figure 1, left), was collected in 2010 from the famous tungsten deposit at Yaogangxian in Hunan Province, China.

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Figure 2. Two scheelite crystals in quartz, image width 2 mm. Photomicrograph by Jaroslav Hyršl.
The specimen contained about 25 small pseudo-octahedral crystals up to 2 mm with an adamantine luster. Most of the crystals were black, but some were colorless. Under long-wave UV light, both crystal types are inert;  under short-wave UV light, the colorless crystals showed a strong bluish fluorescence, indicating scheelite (figure 1, right). Nevertheless, the black crystals were not fluorescent and their edges were red-brown, a typical color for Mn-rich members of the wolframite group, (Fe, Mn)WO4. Raman testing (by Prof. Albert Gilg, Technical University of Munich) identified colorless crystals as scheelite (figure 2) and black crystals as the mineral hübnerite (figure 3), with the strongest peak at 877 cm–1. Their pseudo-octahedral form confirmed their origin as a pseudomorph after scheelite.

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Figure 3. This group of scheelite crystals in quartz was partially replaced by hübnerite.  Photomicrographs by Jaroslav Hyršl; image width 3 mm.

Jaroslav Hyršl is a mineralogist in Prague.