Needing to right click pebbles to pick them up is the last thing I expected for how to obtain them. I tried to break them with and without silk touch, just like any other blocks, and failed, and REI did not show any means of obtaining them, so I assumed they were bugged until I right clicked one while goofing around. I feel obtaining pebbles needs to be made more straightforward. They could simply drop when broken, which is what the player expects. If you really want them to be picked up via right clicking, you should add a REI info tab for them explaining to right click to pick them up so that, when players look for recipes for them, they'll find the info tab and learn how to grab them.