Malachite of the Mountain

Pebble of Earth. This gem has 10 charges and regains 1d10 charges at dawn. While holding the gem in your hand, you can use an action to expend any number of charges. You gain a +1 bonus to your AC for each charge expended until the start of your next turn. When you expend the last charge, roll a d20. On a 1, the gem crumbles to dust.
  Mountainwalker. While this gem has at least 1 charge, and you have it on your person, you are not impeded by difficult terrain while traveling in mountainous regions. Additionally, you suffer no negative effects from high altitude, including elevations above 20,000 feet.