Olivine-rich lava. This lava contains big phenocrystals of olivine (seen here in close up). Olivine is a green mineral found in various igneous rocks and lava. The surrounding lava (upper right corner) is vitreous and black because it cooled down quickly when the rock formed. In contrast, the olivine part cooled down over a longer time period, which allowed the formation of large, visible crystals. This sample is from Lanzarote, the Canary Islands.