Mine-cut diamonds are typically square or slightly oval and have a deeper crown and pavilion, or top and bottom, than modern stones. "Mine cut" does not refer to the place the diamond was faceted, but rather to its overall shape and brilliance.
Before mechanization, the process of cutting diamonds was labor-intensive. To ensure that the work was completed efficiently, employers docked the pay of workers who spent too much time faceting individual stones. Thus, cut diamonds tended to retain a higher proportion of their original material and have the shape that has come to be known as a mine cut.