Thank you for viewing. Stone Name: Dumortierite in Quartz Stone Size: 7mm Inner Diameter: Approximately 16cm Condition: Only tried on Dumortierite in Quartz is said to be the "stone of thought" and the "stone that sharpens concentration." Purchased at Tida Stone in Okinawa. Please note that due to the nature of natural stones, there may be small chips, dents, irregularities, and cracks. This item has been handled by a person, so please understand this before purchasing.