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In reply to the discussion: Earth May Have Underground 'Ocean' Three Times That on Surface [View all]Erich Bloodaxe BSN
(14,733 posts)pressure and temperature regimes. If I take a chunk of carbon, stable here at 1 atmosphere of pressure and room temperature, and put it under a ton of pressure and heat, I can change its structure to turn it into diamond. And this can happen quickly. Going in the other direction, from high to low pressures, that diamond will only degrade very slowly. If I put it in a mix with several other minerals and do the same thing, they'll shuffle themselves around to try and find the arrangement in which they're most stable, and swap out elements to form new minerals. In the crust, that means you wind up with a lot of olivine and spinel like minerals.
Bring them up to the surface, and they'll start interacting with various liquids and gases and be weathered - sometimes into new minerals, although in many cases simply mechanically changed, not chemically, into smaller pieces. Sandstone is mainly just a bunch of compacted smaller pieces of quartz. But throw iron up onto the surface, and it will oxidize over time.
I'm not familiar with ringwoodite structure specifically, but how easily you could break free that hydroxide depends upon how it's attached to the rest of the structure. (And now you've got me wondering if my 20 or so year old 'encyclopedia of mineralogy' even has ringwoodite listed in it...) At any rate, it's certainly possible that the water currently on the surface of the earth actually came from ringwoodite forced up to the surface via tectonic and volcanic processes, and all of those hydroxides chemically shifting at low temps and pressures into water. (the bonds in water are fairly weak - that's why you can do experiments in grade school where you use electricity to break water apart into oxygen and hydrogen.) If so, that puts forward a very intriguing view of the evolution of the planetary surface.