Nara is a metallic green-black stone 30 times the density of steel and the hardest of all D'ni stones.. Nara is created by dumping excavated rock into a huge machine (a fusion-compounder) that reconstitutes its matter, reforging its atomic links to reduce its volume by 200.
In 5307, during the reign of King Me'emen, the Guild of Miners and Guild of Stone Masons worked together and they revealed that created Nara in the laboratories. Nara offered tremendous opportunities for mining and construction and ended up having a massive impact on future opportunities for D'ni. Even at the time of its release, there was apparently much excitement about its potential.
In "The Book of T'iana" the creation of nara is explained as a bi-product of nuclear fusion used to power D'ni mining vehicles. it starts as raw stone/mineral and is put into a machine and a process changes the mineral into caplets to be used in a fusion generator and nara is the bi-product.