Stones changing color?

The one stone is changing color because silver is rubbing off on it. Does anyone know how to clean this off of a stone bead?

We bought two golden quartz at the same time. They were both light gold in color. One has been sitting in a box and one has been worn fairly often. The other day I was trying to figure out the one on the bracelet and then compared it to the other one and the one on the bracelet is much darker. I would say it is half way to a smoky quartz. Maybe this is my imagination but I remember them being the same when new. Has anyone else seen this happen with golden quartz?

I have wundered if the golden quartz is treated like the smokey quartz to get the color.

I have only one golden quartz so I dont now if it changes color.

Ive got two on the same bracelet,but i haven't noticed any colour change,and i wear that one a lot.Have you got any perfume or creams on the stone without realising it,it might be a reaction! It's a bit of a mystery as i have never heard this before,sorry I can't be more help

It is not impossible, but the criteria to achieve such a discoloring seem not in place like heat or radioactivity?

An article that covers color change of minerals:
http://www.minsocam.org/msa/collectors_corner/arc/quartza.htm

This site covers it all though it is a bit of a tough read perhaps:
http://www.quartzpage.de/gen_phys.html

Another interesting page:
http://www.gemselect.com/gem-info/quartz/quartz-info.php

Interesting... maybe heat treated stones can change when exposed to light. Also the porosity of the stones or any moisture/air trapped within and eventually released might case it to change over time. Could be quite cool to have this metamorphosis in a natural stone, providing you accept the possibility it could happen.