"Dried beans are a product of the field and need to visually inspected for small stones, clumps of dirt and bits of foreign matter that are sometimes harvested along with the beans. Any broken beans must be removed as well, because they will not cook evenly. The easiest way to sort beans is on a large white plate. Place a single layer of beans on the plate and remove any unwanted items. After a little practice, this can be done very quickly. Some cooks sort their beans before placing them in storage containers so that they are ready to use at any time.
Next the beans must be washed. Place them in a large bowl or pot and cover them with four to six cups of water per cup of dry beans. (As a general guideline, one cup of dried beans makes approximately 3 cups cooked.) Gently swirl the beans in the water and remove any beans that float. These are hollow and will not cook properly. Pour off the water. If the water is particularly dirty, wash the beans again. Special care should be taken when washing split peas as their starches are exposed and will leach out into the washing water. The washing water will appear cloudy as if dirty, but it is not. Wash split peas quickly to avoid the loss of nutrients and flavor."
Surely if it had a pebble in it then the pebble wouldn't dissolve in the washing water anyway?
Anyway, I am over cautious wrt food hygiene, I wash all normal fruit/veg thoroughly. However if I forgot to wash any sort of fruit or dried item etc and then it was boiled for even 5-10 mins I'd definitely eat it, honestly.