Sorry, I am getting a bit behind on RoW. That's just as well, and I think I will keep the blog a week behind the student competition as they could always find this and use your guesses! And they are in direct competition for geology stickers so we can't have that.
Due to the general troubles with the first two rocks of the weeks (both online and in the office) I decided to try something a bit more accessible to students and internet viewers this week. I present:
And the solution to last week's rock:
This rock is a partially-serpentinised harzburgite from the Franciscan Complex (Ring Mountain), California, USA. Harzburgite is a rock of “depleted” mantle origin. The rock comes from an ophiolitic unit which was thrust over the complex during the Jurassic. The original mineralogy of the rock would have been about equal amounts of pyroxene and olivine. You can still see the grains of dark green pyroxene but the olivine has reacted with seawater to form serpentine (antigorite) and talc. Metallic looking bits come from weathered sulfides and oxides. These minerals weather easily, leaving the surface of the rock rough and yellow in colour.
1. (1 pt) Minerals?
: Pyroxene, serpentine, magnetite
2. (1 pt) Rock name?
: peridotite or harzburgite got a point
3. (1 pt) Tectonic environment?
: ophiolite or subduction zone got a point.
AWARDS OF THE WEEK:
FIRST PLACE: Pia Vigletti for
performing experiments on the rock, even though results are inexplicable
RUNNER UP: Anonymous person for
“Moon rock, that’s why it smells like cheddar”