Fonsager, homeworld of the Stonecutters, was originally a civilized and well-populated Agri world until suffering a series of devastating failures with the planet's numerous nuclear power facilities. The surviving populations were consolidated into a pair of hive cities and put to work producing the weapons and equipment needed by their Space Marine overlords. Meanwhile the Stonecutters had been forced by this planetary catastrophe to move their Chapter fortress to Fonsager's moon, Hertagha. Due to the intensity of radiation still prevelant on Fonsager, mutation is sadly much more common than on most Imperial worlds and the Stonecutters are rarely able to locate suitable new recruits from the planet's population. The Stonecutters therefore select their Initiates from peoples throughout the Imperium, often testing and screening potential candidates from pacified warzones before moving on. Those who pass are sent back to the chapter fortress to begin the process of becoming a Space Marine and where they will eventually be inducted into the Tenth Company, thus becoming an Initiate Brethren of the Stonecutters. For the sake of convenience the Stonecutters also routinely search their neighboring systems for recruits as traveling through the warp from distant warzones is rarely a simple affair.
The tragedy that befell Fonsager occured just shortly after the founding of the Stonecutters and the establishment of the planet as their Homeworld. In recognition of the disastrous turn of events on their once beautiful world, the Stonecutters abandoned their original heraldic colors and switched to the dark reds seen worn by them today. In remembrance of their early history, it has become custom for those exceptionally rare Brother Marines drawn from Fonsager's native population to paint their power armour in the chapter's initial colors, but otherwise devoid of chapter insignia or squad markings. In accordance with an edict issued by the first Chief Librarian of the Stonecutters, no more than one such Marine may ever be assigned to each Company at any one time. As a practical matter, however, this has never been a problem due to the low percentage of recruits from Fonsager, typically occuring with a rate of less than one per one hundred Initiates that survive to become Battle Brothers of the Chapter. The Scouts of the Tenth Company are never given this honor regardless of their ancestry or parentage, as it believed that the Initiates must first prove themselves worthy of even wearing a suit of sacred power armour. Great things are expected of those Brother Marines who wear these ancient colors and the induction of such a Marine into one of the Battle Companies is a solemn and portentious occasion laden with much ritual, fasting, and meditation.
Since its successful conversion into an industrial hive world, Fonsager is still able to serve the Stonecutters with the output of its manufactorums and weapon forges. The harsh environment that covers the majority of the planet's surface also provides to the Chapter's recruits excellent conditions for survival training, as well as the opportunity to engage in some dangerous combat exercises. There still lives amongst the ruins of Fonsager's old cities significant populations of the heavily mutated descendants of those who were exposed to the worst effects of the nuclear calamity but somehow managed to survive. These unfortunate people were subsequently deemed to be too high risk to be brought into the newly formed hive cities, instead being simply left to live and die in the shattered remains of their previous existence. What has survived to the present day, and in some areas even flourished, is a horribly gruesome race of degenerate cannibals known as the Ghestrani against whom Stonecutter recruits are frequently tested. Were it not for their value as opponents for these young Marines, it is likely that they would have been exterminated entirely by agents of the Imperial Inquisition who remain understandably wary of allowing these abominations any space within the Emperor's realm.