Bloodstones enable Legates to draw upon more power than they could otherwise
Many Legates who are channelers carry Bloodstones somewhere on their person. These stones are tied to how they channel magical energy.
As far as GURPS rules go, Bloodstones are identical to Powerstones.
Bloodstones are deep blood-red gems, cloudier than rubies, which sometimes shine with an eerie light all their own.