Named after its founder, Sid Pieters, in 1962 when it was first discovered in Namibia, then later in the Human Province of China in 1993, Pietersite is known for its whimsical, thunderous patterns and a spectacular visual effect known to gemologists as chatoyancy.
Pietersite’s main constituent is a blue, gold and/or red mineral called Crocidolite, a pseudomorph that is also responsible for the golden silky gemstone Tiger Eye. A pseudomorph refers to substitution form one mineral to another whilst retaining the original appearance and dimensions. In the case of Crocidolite, a form of asbestos, quartz (silica) replaces the fibrous mineral remaining true to its fine, dense needle-like structure.
The parallel arrangement of the silicified asbestos fibres creates a distinctive sheen known as chatoyancy, where the silky play of light reflects from the beneath the stones’ surface. Bunny Bedi, owner and designer at Made in Earth, explains how this effect is best captured when cutting.
“In order to see the chatoyancy at its most brilliant our cutters need to be vigilant to ensure the biggest areas of fibres are parallel to the base of the cabochon.” Bunny continues, “Safety must also be considered in case areas of unadulterated rock create airborne fibres of asbestos – for this reason a mask must be worn whilst polishing Pietersite or any mineral containing Crocidolite”.
“Although Pietersite can come in a small variety of colours and combinations, the blue hues from a light grey tone through to a deep midnight navy, that are mined from Namibia, are most prized and desired by our customers”, Bunny explains. “When found with patches of golden brown the contrast can be a stunning display which visually increases the intensity of the blue.”
The golden colour in Pietersite is due to the oxidisation of Crocidolite during its formation with the presence of iron. We have some amazing Pietersite rings and pendants where you can see this beautiful play of colour.
Although it has the chatoyancy of Tiger Eye, Pietersite is not usually found with a constant directional structure of bands and fibres but rather in swirls, swathes and segments. Crystallising in masses, this mineral has been stressed, folded, fractured and broken apart during the earth’s geological process. The fibrous materials have been reformed and naturally re-cemented together by quartz and occasionally with parts of jasper – a cryptocrystalline variety of quartz. This formation creates a brecciated aggregate with a rather chaotic pattern of bold, multi-directional strokes of fibres giving it its reputation of a ferocious, thunder bound sky.