Pietersite

Gem-quality pietersite is known from two main sources. In Namibia it was found in rounded dolostone cobbles on farmland near Outjo, in the Kuraman district (Mindat lists Hopewell Farm 240, Outjo, Kunene Region); researchers interpret it as a solution breccia formed when silica-rich fluids dissolved and replaced the dolomite, after which crocidolite grew from reactions between chalcedony and hematite. In China it comes from Xichuan, Henan Province, where it was discovered in 1966 during prospecting for crocidolite (another source reports a similar rock from Nangang, Hunan Province). By 2010 both mining areas appeared to be closed, although material continued to reach the market.

Pietersite is recognised by angular chatoyant fragments cemented in irregular patches, giving swirling, storm-like flashes instead of the continuous parallel bands of tiger's eye. Its refractive index (about 1.54) is that of quartz. Namibian material is mostly blue-gray and golden yellow with a lower specific gravity (2.50–2.58) and usually fluoresces green under UV light; Chinese material is mostly jasper-like brownish red with weaker chatoyancy and a higher specific gravity (2.67–2.74). Open spaces in some polished pieces have reportedly been filled with wax or glue during finishing.

Jewelers commonly recommend cleaning these tiger's eye–related materials only with a polishing cloth rather than alcohol, steam or an ultrasonic cleaner, and note that they chip or break more readily than many gems when struck.

Pietersite is named after Sid Pieters, a gem and mineral dealer who first described it in 1962 after finding it while prospecting near Outjo, Namibia. He registered the gem in the mineral records of Great Britain in 1964 and brought it to market in the 1970s; by 1996 much of the minable Namibian stock was reported to be depleted. Chinese pietersite, discovered in 1966, was mined in the 1970s and 1980s but reached the market only in the 1990s. The Japanese retailer Pascle explains the alternative name Tempest stone by its storm-like pattern.

The Japanese retailer Pascle says pietersite is believed to give its owner a chance to look at themselves objectively and to sharpen intuition and insight, and it markets the stone as a charm for reaching goals, such as in exams or at work.