Another famous Japanese inkstone is the Ogatsu. The stone is a dark grey-black stone, to pure black. It is a type of slate which lends itself well to detailed carving. The stone is about 200-300 million years old, and is quarried in Kitakami mountain, near the city from which these suzuri take their name.
This video shows the carving of a traditional suzuri.
According to the website http://www.kougei.or.jp,
. . . the origins of the Ogatsu inkstone can be traced back to the Muromachi period (1392-1573). Then, at the beginning of the 17th century, two inkstones were presented to the military commander, Date Masamune, who was on a deer hunt on Toojima, an island off the Ojika Peninsular. It seems that he was highly delighted with the stones and reciprocated generously. Date’s son, Tadamune, also recognized the skill with which these inkstones were fashioned and engaged craftsmen to make inkstones for the clan. It then seems that he placed the mine from which the stone was sourced under a monopoly and did not allow outsiders to mine there.
The most important part of an inkstone is the houbou, or bed on which an ink stick is rubbed in a little water. It is the texture and perfect degree of hardness of this surface which is a particular feature of the Ogatsu inkstones. The stones are made from a type of slate and are either black or a deep indigo in color, have a rich luster and a smooth surface. Some highly fashioned, others are almost as they were mined. In all, 26 firms employ 88 people who are engaged in making these inkstones and there are also 4 government recognized Master Craftsmen.
These stones are elaborately carved, with lids, as well as left in a more natural shape. The photos below gives you an idea of the range in which they are produced.