Hornblende picrite: The minerals in picrite often decompose quite quickly. Olivine is replaced by green, yellow and red fibres of serpentine, while augite is replaced by chlorite or hornblende. Only hornblende remains unaltered, creating hornblende picrite. Many ancient picrites are like this, such as those found in Gwynedd and Anglesey in Wales and on Sark in the english Channel Islands.