As a geologist, I'll be paying particular attention to some extensive rock outcroppings and railroad cuts on my layout. I've been looking at some the rubber rock molds that are available, and some look to be good for this. But I'd need a variety of types, and the expense of buying them new from, say, Woodland Scenics, builds. So, I'm wondering, once people have built their layouts, and have used these molds, what do they do with them? Certainly they are fairly durable. Surely, not every modeler buys a new set of these molds just to be used a few times. Does anyone here have any used molds that s/he would be interested in selling? Another approach is to make my own molds, using real rocks and some sort of rubber molding material. Has anyone had success with this technique? I've been having lots of fun ideas about rocks -- modeling type localities (the geologist's term for "prototype") and marine transgressive sequences and the like. The cutaway back of the mountain could have fun things going on inside - a coal mine, a tourist cavern, a geologic radioactive waste disposal facility (my personal favorite). Any fellow geologists out there?