Quartz with acicular emerald inclusions
Author: Gagan Choudhary
(This article was first appeared in Gems & Gemology, Vol. 47, No. 4, pp 323)
Quartz with randomly distributed tourmaline and/or rutile needles is widely available in the market. These gems are often described as “tourmalinated” or “rutilated” quartz, respectively. The author had a chance to examine a quartz specimen that contained eye-visible emerald crystals (figure 1). Although intergrowths of emerald and quartz and a notable emerald-in-quartz specimen have been reported previously (see e.g., Gems & Gemology, Lab Notes: Summer 2000, pp. 164–165; Fall 2008, p. 258), this specimen was quite different.
Figure 1: This 45.85 ct quartz cabochon was unusual for its eye-visible inclusions of elongated emerald crystals
The light smoky 45.85 ct marquise-shaped cabochon measured 37.60 x 18.26 x 11.57 mm. The prominent green inclusions displayed an acicular habit (figure 2, left). The green colour and hexagonal profile (figure 2, right) strongly suggested emerald, but their acicular habit raised some doubts, as emeralds typically show a more columnar habit. Most of the crystals also displayed basal parting planes, reminiscent of the actinolite blades found in emeralds from the Ural Mountains of Russia. Some also displayed colour zones following the prism faces, while others contained rain-like inclusions.
Figure 2. The inclusions displayed an acicular habit (left, magnified 32x), which is usually not associated with emeralds. However, their green colour and hexagonal profile (right, magnified 48x) helped identify them as emerald. Also note the green coloured polishing powder present in some of the open fractures.
To conclusively identify the inclusions, the sample was examined under a desk-model spectroscope. It revealed a spectrum consistent with emerald, featuring a doublet in the red region and an absorption band in the yellow-green region. Further confirmation was obtained by FTIR, which displayed a typical emerald spectrum. IR spectroscopy also confirmed the host material as quartz, which was supported by a spot RI of 1.54 and a hydrostatic SG of 2.65.
Textural relationships indicated that the emerald crystals formed before the host quartz (i.e. they are protogenetic). Emerald is known to occur within quartz, but this sample was quite unusual for the crystals’ acicular habit and their occurrence as inclusions, not merely in association with the quartz or as an intergrowth.
All photographs and photomicrographs by Gagan Choudhary