
THE MATERIAL
These 100 mm (3.9 in) in diameter and 1 mm (0.039 in) thick discs are made of industrial sapphire. At 9.0 on the Mohs hardness scale, sapphire is one of the hardest known materials, (compare with diamonds, a 10 on the Mohs scale). Sapphire can withstand the extreme temperatures of the lunar surface and remain unaltered over time.
The information is physically micro-engraved without coding. The legibility of the engraved data is therefore not dependent upon future technological innovations.