They look very similar to small pebbles commonly found on beaches, but who can really say for sure, they may be fragments of an ancient alien spacecraft that crashed to Earth millions of years ago -- I prefer to think of them as the latter. Whatever the case may be those objects are clearly very old, civilizations rose and fell, species came into existence and then died out all while these objects sat undisturbed somewhere. You are likely the first human being in history to intentionally observe and collect those pebbles/possible alien spacecraft debris.