In September 2011, GIA was informed by Dudley Blauwet (Dudley Blauwet Gems, Louisville, Colorado) about a new find of citrine, which was represented to him as natural-color material from the Kitwe area of Zambia.
He obtained ~1 kg of the rough at the 2011 Tucson gem shows, and faceting of 208.5 g of rough yielded 29 stones totaling 268.08 carats. Four of the stones were concave cut, and the largest one weighed 48.69 ct.
Mr. Blauwet loaned seven of the cut citrines to GIA for examination, ranging from 3.38 to 43.86 ct. The color of the citrine ranged from pale slightly brownish yellow to brownish orangy yellow, and the seven stones showed the following gemological properties: RI—no = 1.542, ne = 1.552; birefringence—0.010; hydrostatic SG—2.65–2.66; UV fluorescence—inert to both long- and short-wave UV radiation, except for one pale yellow sample that fluoresced very weak white to long-wave UV; and no features seen with the desk-model spectroscope.
Microscopic examination revealed straight and angular color zones, as well as a general haziness and bands of hazy particles, which proved natural origin and were similar to those previously described in citrine from Sri Lanka. The 3.38 ct stone also contained a plane of parallel tubules and two-phase inclusions. Viewed with cross-polarized light, minor areas of Brazil-law twinning were seen in only the two smallest samples.
Natural-color citrine is relatively uncommon compared to other quartz varieties such as amethyst and smoky quartz. Assuming that the coloration of this citrine is natural—as represented by the supplier—this large, clean material makes a nice addition to the gem market.
Image: These concave-cut citrines weigh up to 43.86 ct and show the range of color from the new Zambian deposit. Photo by Robert Weldon.
Courtesy of GIA (Gemological Institute of America) © 2012.