Granted. It is infinitely rigid though, causing some paradoxes.
A) Since speed of sound in material is based on it's rigidity, the speed of sound in Adamantine is infinite.
B) If 2 pieces of adamantine strike each other, as they can not deform even a little bit, they have to stop (relative to each other) at the spot. This means also stop in 0 time, giving the collision infinite power. This means that whenever 2 or more pieces of Adamantie touch, there are nuclear blasts.
C) Being infinitely rigid, it's particles can not move relative to each other. This means it theoreticaly has 0K temperature. But as it can not absorb any heat, it always acts as if it had the same temperature as whatever touches it. All radiation is completely reflected from it.
I wish to have a nuclear shelter coated with Adamantine. Large enough for 5000 people to live comfortably with enough supply of food, water and energy to last them 1000 years. Also, the nuclear power plant and radioactive material storage are in 2 compartments, separate from the other areas, which are also coated in Adamantine. Any places, where 2 or more pieces of Adamantine could meet on or in the shelter have a 5cm layer of lead filling between the pieces of Adamantine. On the outside, this filling is covered by ceramic plating.