I picked up some very interesting rocks and pebbles on the beach in Malaga, Spain this summer. They are predominately flat and colored dark grey crisscrossed with stripes of orange and white. The dark grey area looks a bit grainy. I was able to make a faint scratch with a stainless steel table knife, but not with a U.S. quarter.
I'm not really a rock hound but I like to collect interesting things for macro photography. I'm curious to know more about these pretty little stones. I Googled for information about rocks and geology of the Malaga area, but couldn't find any pertinent discussion. However, if you Google "Camino Del Rey Malaga" you'll see similar color patterns in the canyon walls.
I apologize that I did not include a scale in this photo but this rock is approximately 2 inches (5 cm) on its longest edge and quite light in the hand (30g according to my kitchen scale). There were rocks like this of all sizes on the beach, from tiny pebbles to much larger stones. I even noticed similar grey, white and orange boulders in the fortifications and walkways around the Malaga castle.
My guess is that this is some sort of volcanic rock shot through with quartz, but I don't know what creates the orange color. (I apologize for not knowing the proper terminology). Anyway I would be grateful for any thoughts from the experts.
Here are a couple other ones: