Overview and images of dunite as a rock type are here: Dunite
I also have similar photos of a similar rock. My sample is from Lanzarote, The Canary Islands. It is a xenolith of a dunite? As a mineral aggregate this green stuff in basalt definitely qualifies as a dunite but I was not sure whether it comes as a xenolith from the mantle or is it an olivine cumulate rock formed in the crust. Hence, my question was: is it necessary for a dunite to form deep below or do we only need the rock to be phaneritic and composed of more than 90% olivine? I tend to think its a xenolith because it seems to be surrounded by basalt from every direction.
I got few responses. The consensus seems to be that the rock must be >90% olivine to qualify. I think its a reasonable way to look at it because we often really don’t know and can’t possibly know how a particular rock sample came to be. The Canary Islands, for example, have bneen extensively studied. It is clear that there are very complex interactions and the source(s) of the ultramafic rocks remain often uncertain. Dunite inclusions may be foreign to the host carrier (xenolith) or there might be a genetic link (inclusion).
Here are the pictures of the same rock from different angles:
Dunite xenolith in basalt from Lanzarote. The width of the hand sample is 9 cm.
Dunite xenolith in basalt from Lanzarote. The width of the hand sample is 11 cm.
I have written about somewhat similar rock before: Olivine basalt from Oahu.