Malachite of the Mountain

Pebble of Earth. This gem has 5 charges. It regains all charges at dawn. While holding this gem in your hand you can use a reaction 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. If you hold the gem in your hand while it has at least 1 charge remaining, you are not impeded by difficult terrain while traveling in the mountains and suffer no negative effects of being at a high altitude, including elevations above 20,000 feet.