Friday Rock Blogging: Gabbro
I know it’s getting rather late in the Friday for some of you; sorry about that. I was thinking that I’d finally throw up a few pictures of gabbro and explain this blog’s name, but when I went looking for pictures, well, I remembered why I’ve been putting it off. Then I was somehow distracted by the poor quality of Wikipedia’s tectonic plate entries – there’s some implicit libel of the Galapagos Rise going on there. Really, I should stop browsing the geology stubs, it wreaks absolute havoc with my anal retentive inner demons.
Anyway. Gabbro is a very unassuming sort of rock. It’s the intrusive equivalent to basalt – same stuff as here, but because it forms underground, it cools more slowly and forms visible crystals. It’s not green. Its primary components are plagioclase, amphibole, olivine, and pyroxene – white, dark, green, and dark, respectively. In general, if a gabbro contains so much olivine that the overall rock appears any greener than a dull green-gray, it gets classed as a peridotite.
But, I place way more value on alliteration than I do on truth, so there.