A ring taken with the sword
The French explorer Henri Duveyrier wrote in 1864 that every Tuareg man except the marabouts (Muslim holy men) wore a stone ring on his right upper arm from the age when he could take up arms, and never took it off. Its purpose, the Tuareg told him, was to give the arm more strength for a sword stroke. He described the rings as green serpentine. In 1930 the anthropologist C. G. Seligman wrote that at 16 or 17 Tuareg youths began to carry a sword and wear the stone arm-rings, and were then counted full members of their tribe or village.
To verify: The page number of Duveyrier’s section on the stone ring: the scanned contents and page headings disagree.