Professional Jeweler Archive: Trapped During Construction

November 2000

Gemstones & Pearls:/Gemology

Trapped During Construction

Negative crystals in quartz often contain gas, liquid and solid inclusions

Quartz sometimes contains bizarre negative crystals that look like miniature models of their host. Other times, the negative spaces take on other shapes, and often they’re linked by channels.

These inclusions are most often found in rock crystal quartz, but can be found in amethyst as well. In fact, some other gem species can have negative spaces also, including diamond, beryl and topaz.

Imitating Shapes

Quartz grows in a rombohedral crystal shape (as shown in the top photo). The negative crystals that imitate the crystal shape of their quartz host often appear complete with hexagonal pyramids at both ends. (These negative crystals, and their hosts, are described as being doubly terminated.) Spaces that don’t mimic the gem’s exterior shape are called voids.

From the Host

Generally, the spaces contain gas, liquid and solid inclusions that were trapped as the crystal grew. The liquids and minerals were precipitated out of the host crystal and into the negative crystals and voids during the quartz’s hydrothermal formation, says John Koivula, chief gemologist at the Gemological Institute of America. For anyone interested in negative crystals, Koivula recommends reading Fluid Inclusions by Edwin Roedder (Reviews in Mineralogy Vol. 12, published by the Mineralogical Society of America, 1984).

– by Robert Weldon, G.G.

The quartz crystal from Mount Ida, AR, contains several negative crystals and voids.
The same gem at 10X. Negative crystals can contain liquids, solids and gases.
The same gem at 40X. Negative crystals in quartz seen here are doubly terminated rombohedrons.
All Photos by Robert Weldon

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