The act or process of obtaining a core sample of rock material using a diamond-inset annular bit as the cutting tool. This tubular bit and attached core barrel are rotated at a speed under controlled pressure by means of hollow steel, flush-jointed rods through which water is pumped to cool the bit and remove rock cuttings. With the advance of the bit, a cylindrical core of rock passes up into the core barrel, where it is held by a core lifter or other device.