An interesting theory...
But, having seen thousands of similar things while doing terrestrial field geology, I tend towards a non-electric explanation.
One of the best (I think) geologic Mars websites is marsgeo.com. The author posts here now and again and while I may not always agree with everything he writes (geologists never completely agree), he has done a nice job at compiling information into easy to read articles.
See especially:
Opportunity RockTypes
And specifically:
Hedges
However, acids in contact with metals often have interesting electrical properties!