Deep Stone is the colloquial name for the excretion (or final form) of a bacterium native to the Beaufort Sea called Profundacillus Deulucidus. It seems to be the raw form of the more refined truStone.
Unrefined deep stone was found by the Reach scientists to give off an energy that naturally augmented human healing processes and extended human lifespans. When refined, presumably into truStone, this energy had a greatly magnified effect on human subjects. This energy was dubbed truLight. In conjunction with the mineral known as ceterite, "cells" of truStone were constructed into beacons capable of extending truLight radiation over a large area. Exposure to truLight, however, was found to cause a dependency later known as "Beacon Addiction."
Animal subjects had a varied, even random, response to truLight and deep stone energy which did not seem to follow any logical pattern across species.
A drug developed from deep stone, marketed as "Truth & Beauty" by truCorp, was the cause of the emergence of the Sennin through an unknown interaction with the father's gamma-seminoprotein. Sennin were discovered, through the chaos of the L.A. Riots, to be capable of some interaction with truStone cells due to their own emission of truLight.