#dolerite

Faults in the greenstone dolerite cliffs are seen at several locations on Isle of May, Scotland.

These rocks have all experienced hydrothermal alteration and contact metamorphism. The 1.4 billion year old Velkerri Formation from Australia is an organic rich mudstone. Some time after burial and lithification, the rock was intruded by hydrothermal fluids that caused metallic sulphide, and ferrous carbonate + quartz mineralisation. I think some maybe related to the intrusion of dolerite around 1.2 billon years ago, and some related to basin inversion around 800 million years ago. The mineralisation and contact metamorphism is widespread but in some areas is subtle and only visible on the microscopic scale. The velkerri formation is the basis for much of what we know about marine chemistry during the early evolution of eukaryotic life. Several important geochemical studies sampled the velkerri formation and used the pyrite in particular to show that the oceans 1.4 billion years ago were low in oxygen and rich in sulphur. This environmental state is thought to have been a major barrier to the development of more complex eukarotes. However, the hydrothermal and contact metamorphic alteration, in particular the micro scale alteration were unknown when these studies were conducted. As these previous studies used bulk sampling methods, it's likely that they unknowingly sampled the later sulphides which will have influenced the results and the interpretations of the previous researchers. This does not mean the previous work is bad and should be disregarded. Simply that the results should be reinterpreted inlight of this new information. That is how science is supposed to work. It is self revising and correcting. That is how science advances and improves. However, getting paper reviewers to understand and accept this is another thing entirely. I'm currently revising this work after a rejection. So let's see if the next version is enough to get the paper out. 😉 #geologyjohnson #geology #geologyrocks #pyrite #blackshale #shale #ore #hydrothermal #igneous #dolerite #metamorphism #science #sciencerocks #earthscience #naturalhistory https://www.instagram.com/p/CdaMy8-sFoZ/?igshid=NGJjMDIxMWI=

A Miocene dolerite sill sitting over volcanic sandstone....assigned to a divine place at the shore.

2018: Jurassic dolerite is seen intruding sedimentary rocks of the Parmeener Supergroup (mainly Permian and Triassic) along the Three Capes track on the way to Cape Hauy.

Dolerite columns and cliffs, Bruny Island, Tasmania. 

apollo bay house ~ room 11 | photos © ben hosking

(They're all dolerite/diabase...) I feel like I used to be able to tell clinopyroxene and olivine apart no problem. But nowadays it's more like--"follow your heart it will guide you to the truth." I guess it doesn't hurt to err on the side of less cpx, since it would be the first to totally be taken out of the melt?