This type of armor was originally developed near the end of the Nanoswarm era and has evolved into many different forms and specialities since it's creation. It combines protection from high-powered weaponry with close combat armor and defenses against gray or khaki goo attacks. This armor type gets its name from the thick biont bones that it resembles.
The construction of the armor is as follows:
1: The outermost layer is a combination of diamondoid and other hyperstrong materials. They are laminated together so as to rob a projectile of force by causing it to expand between the layers and possibly plug its own hole. The armor is also polished to a high mirror shine and covered with irregular organic ridges. This texture can deflect incoming projectiles and melee attacks. The ridges can also defocus an energy beam and diffuse its power.
2: Inside the hard outer layer is a spongy mid-layer. The "marrow" is loaded with nanofabrication systems and nanite storage cells. When the armor's integral sensors detect damage to the structure these systems send repair nanites to patch any damage to the outer laminate layer. The system will push blue goo through nano-capillaries on the surface of the armor to combat attacking nano agents before they get through the outer layers.
3. The innermost layer of armor is a diamondoid laminate that is thicker than the exterior layer. This hopefully prevents any further penetration past the armor. The inner layer is often laced with boron, lead or some other material that is suitable for radiation shielding.
Some forms of Marrowbone Armor have an exterior layer that is coated with a black ablative material. This substance is a thick, rubbery polymer that absorbs energy extremely well. The material quickly boils off when superheated by an energy weapon like a laser. It can even shed hot spots quickly by popping off blisters of material through steam pressure. The ablative layer forms a stiff skin in contact with air, thereby leaving the looser energy absorbent material free to boil and build up pressure to remove the energy quickly. This can cause burns to anyone who is standing too close when the ablative layer flash-vaporizes or pops a blister. This variant can be regenerating with a modification to the "marrow" of the armor. Other outer coatings include thin layers of programmable matter that provide excellent shielding from EM-based attacks (i.e. lasers and masers).