Pietersite
Discovered by Sid Pieters in 1962 Namibia, it bears his name.
It is a breccia aggregate consisting mainly of hawk's eye and tiger's eye that belongs to the branch of tiger's eye called Riebeckite. This is a pseudomorph, a mineral that has the morphology of a preexisting one, which it has replaced due to structural changes, chemical alteration or substitution, or dissolution and filling.
Tiger's eye appears in the form of crocidolite, a form of asbestos (a group of 6 fibrous metamorphic minerals).
When quartz replaces crocidolite, it takes the form of the fibrous mineral that is the cause of the 'chatoyance' (the silky shine concentrated in a fine band of light that changes position as the mineral rotates).
Pietersite does not present the ordered structure characteristic of tiger's eye since during the formation of the crystal, the materials that compose it were broken, swirled, reformed and finally cemented with quartz. Stones and crystals that go through this process are called brecciated.