In the real world, rock formations come in every shape and size. Mother Nature seldom does the same thing twice. Fortunately for model railroaders, there are almost as many ways to model these rocks on our layouts.
Rock can be carved from foam or plaster, or poured into molds. Another fast, and often free, method involves using ceiling tiles. You've probably seen these around your office, or maybe in your own basement. Hung from a suspended ceiling, these pressed fiberboard tiles are cheap, easy to cut and (fortunately for us) easy to break. Since we'll be breaking the tiles to make our rock, you may be able to procure a lifetime supply in a few broken tiles from the scrap bin. Fear not however, as a new tile will only cost a few dollars.
Studying the Prototype
Modelers will spend hours studying photos of locomotives to determine details and weathering. Our scenery shouldn't be any different.
The ceiling tile method is best suited for recreating stratified rock. That is, rock that appears in layers. Such an effect is often found in rock cuts along railroad tracks and highways. Layers of different minerals may even take on distictive coloration. These colors are brilliant at first, but can weather and dull over time.
There is really no great science to making the rocks themselves. Just break the tile. Snapping or tearing chunks out of the ceiling tile will yield a jagged and irregular edge. The closer you hold the tile to the break, the tighter the grain will be.
Break a pile of tiles and you'll have lots of material to work with in the coming steps. The 1/2 inch thick tiles can be used individually or stacked to create taller strata.