Are weapons and armor made of Mithral or Adamantine considered magical?

In a recent dungeon crawl, I was ambushed by some grey ooze. The ooze managed to land a couple successful hits on me, which would normally cause my armor to degrade. However, I was using a set of mithral chain mail that I had found in a previous session. I know that the statistics for mithral and adamant items are found in the DMG, which leads me to believe they are magical, but their descriptions don’t really imply that they are magical.

Is the mithral armor considered magical for the purpose of resisting effects like degrading from the ooze? I also know that adamant armor and weapons exist in our game. Would they follow the same ruling as mithral?