From Merelani, Tanzania New Era Gems offers you a this piece from a limited supply of natural unheated Blue/Purple Tanzanite Rough, The holy grail of Tanzanite Rough. This piece of carefully selected gem material weighs 13.00 cts and measures 12x10x8mm and is offered to you for your cutting pleasure! We believe that the natural blue color is caused by thermal heating in the ground over millions of years, Now that is a slow cooking process!