Most diamonds are found in primary sources, that is, mines, in Africa, Russia, Australia, and Canada. Their journey started about ninety miles below the surface one to three billion years ago, under 2000-degree (F.) heat and extreme pressure. From there they were carried upward to the surface by deep volcanic action.
But sometimes they have been carried by rushing waters to active or ancient riverbeds, or onto shores of beaches or even into seabeds, all of which are called alluvial deposits. Diamonds from these secondary sources are almost always of high quality because, through the action of running water, highly included stones are broken up while ones of higher quality remain intact.
So it is with us.