Although rocks are pretty generic and can be used in any other tabletop game as well, I felt the need to embed them into the Star Wars universe in some form. After seeing rowdyoctopus's pics of the demo tables at Gencon I knew exactly what to do. If there's something like a "typical Star Wars rock concept", it's Ralph McQuarrie's original Dantooine concept art that was later used for EU Alderaan lore and the design of Lothal in Star Wars Rebels.
´Time to get started: I stacked a couple of pieces of foam board and stuck them together using wood glue and wooden barbecue skewers. After letting them dry I used a box knife to work out the basic shape. Sandpaper was used later in the process to smoothen rough areas. You don't have to worry too much about the surface of your rocks at this point, since you're going to sandcoat them later on anyways.
For giving them a sandstone look and feel, I coated the entire rock with a mix of wood glue, acrylic colour (just some dark sandtone), bird sand and some leftover acrylic sealant which I still had from creating the gaming mat (This one is highly optional...)
For detailing, I mixed the base colour with a variety of yellow, red and brown pigments. Even if it's "just a rock" it should never been just grey but have a variety of earth tones in it. The original McQuarrie/Lothal concept uses green to give the surface some depth. Since I'm going for a Jedha-inspired desert terrain, I stuck with the colours I already used for the mat.
After that, it's just some final drybrush with your basecolour + a little white and you're done: Some basic rocks that should have some Star Wars feel to them.