Micro-World Gems & Gemology, Spring 2025, Vol. 61, No. 1

Copper in Indonesian Chalcedony

John I. Koivula and Nathan Renfro

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Figure 1. Left: Containing abundant amounts of native copper but no secondary copper minerals, these two chalcedony quartz cabochons, weighing more than 40 ct each, come from Lawang Kori, West Java Province, Indonesia. Right: This 16.91 ct chalcedony cabochon from Obi Island, Indonesia, on the other hand, contains secondary copper minerals including turquoise blue chrysocolla, green malachite, and a small amount of deep red cuprite. Photos by Annie Haynes (left) and Rhonda Wilson (right).
 
Figure 1. Left: Containing abundant amounts of native copper but no secondary copper minerals, these two chalcedony quartz cabochons, weighing more than 40 ct each, come from Lawang Kori, West Java Province, Indonesia. Right: This 16.91 ct chalcedony cabochon from Obi Island, Indonesia, on the other hand, contains secondary copper minerals including turquoise blue chrysocolla, green malachite, and a small amount of deep red cuprite. Photos by Annie Haynes (left) and Rhonda Wilson (right).

The authors recently examined two oval double cabochons consisting of chalcedony quartz, each with a multitude of glistening metallic native copper inclusions (figure 1, left). These gems were reportedly from Lawang Kori, Garut Regency, West Java Province, Indonesia, and weighed 43.04 and 46.68 ct, respectively, with corresponding measurements of 30.78 × 20.46 × 7.88 mm and 36.21 × 23.19 × 7.88 mm.

Figure 2. The chalcedony cabochons from Lawang Kori, Indonesia, contain an abundance of elemental copper but lack brightly colored secondary copper minerals. Photomicrograph by Nathan Renfro; field of view 5.63 mm.
 
Figure 2. The chalcedony cabochons from Lawang Kori, Indonesia, contain an abundance of elemental copper but lack brightly colored secondary copper minerals. Photomicrograph by Nathan Renfro; field of view 5.63 mm.

A chalcedony deposit was previously reported on Obi Island, Indonesia (J. Ivey and B.M. Laurs, “Copper minerals in chalcedony from Obi Island, Indonesia,” Journal of Gemmology, Vol. 38, No. 5, 2023, pp. 512–521), producing material containing an abundance of azurite, chrysocolla, cuprite, malachite, and other secondary copper minerals (figure 1, right). However, these secondary copper minerals are absent in the Lawang Kori material (figure 2).

This new material is ideal for cutting and takes an excellent polish, which should make it a marketable variety of chalcedony.

John Koivula is analytical microscopist, and Nathan Renfro is senior manager of colored stone identification, at GIA in Carlsbad, California.