Photoelectric Rock Surfaces

Well the first thing you would have to isolate the rock from ground....then test with a multimeter...probably not much current...Do you have any Amethyst, because you can sell that....I ask because I have heard that manganese makes the quartz purple...

http://www.rockhoundingar.com/experiments.php

We have lots of quartz here - chert, jasper, agate, carnelian etc... but I haven't seen any amythest personally in this area. The rock with manganese is afaict a sandstone and splits into fairly flat faces, and what appears to be a thin layer of manganese within...

I guess I should set one up with a meter and wait for the sun to shine. Those sticky electrodes look useful! for a rock.

I had some amethyst and put it in the garden because it was pretty. Well, the sunlight bleached it out, so now it's plain old ordinary quartz. As an experiment, I took it inside and wrapped aluminum foil around it so it was in complete darkness for a few weeks, just to see if the reaction was reversible. Nope, it's still clear.

According to this, it is iron in the quartz that turns it into amethyst, but manganese in glass that turns beach glass purple. It also says the purple in quartz comes from irradiation. Maybe I can find a radium dial clock or watch in an antique store, or maybe take it on an airplane and let TSA x-ray it...

http://www.geologyin.com/2018/05/what-causes-purple-color-of-amethyst.html

If you know somebody that works in a hospital you could get them to store the crystal in the x-ray room....might take a while....or maybe a friendly dentist...

I'm not sure what they are describing here. Do the illuminated rock surfaces acquire a charge which flows to dark areas or different kinds of rock surfaces? Is there a return path so that it can keep flowing or does it just flow momentarily when the illumination changes? (You have to pay to see the paper...)

I don't think that you can expect much voltage. The average photon of sunlight (550 nm) is about 2.25 electron volts, so subtract from that however much energy in electron volts that it takes to free it.

I couldn't read the paper either. They did say it "turns on" in sunlight and "turns off" as soon as that is gone. I also wondered what the direction of flow would be... maybe the incident angle would determine that?

I suppose a very low voltage might be suitable for what they proposed, a driver for geochemical reactions over long time spans. Not much fun for McGyver in that.