Chaoite

Chaoite, or white carbon, is a mineral described as an allotrope of carbon whose existence is disputed. It was discovered in shock-fused graphite gneiss from the Ries crater in Bavaria. It has been described as slightly harder than graphite, with a reflection colour of grey to white. From its electron diffraction pattern, the mineral has been considered to have a carbyne structure, the linear acetylenic carbon allotrope of carbon. A later report has called this identification, and the very existence of carbyne phases, into question, arguing that the new reflections in the diffraction pattern are due to clay impurities.