I couldn’t verify a Roblox-specific “Prison Mine” gem guide from the available results, but in most prison/mining Roblox games, gems are usually a premium currency used for boosts, upgrades, or skipping timers.

How gems are usually used

  • Open the shop, upgrade, or premium menu.
  • Spend gems on things like:
  • Mining boosts or luck boosts.
  • Backpack, pickaxe, or storage upgrades.
  • Rebirth, rank, or zone unlock shortcuts.
  • Limited-time items or event rewards.

What to try in your game

  1. Check the shop or store icon.
  2. Look for a gems tab or a button labeled use , spend , or redeem.
  3. Tap an item and see whether the game asks for gems instead of coins.
  4. Check the daily rewards , codes , or events menu if the game has one.

If nothing happens

  • Some games only let you use gems after reaching a certain level or unlocking a zone.
  • Some games require you to buy items from a specific machine, not a normal shop.
  • If “Prison Mine” is actually a different game title, the gem system may be unique to that game.

Best guess

If you mean a Roblox prison/mining game in general, gems are probably there to speed up progress or buy special upgrades rather than basic mining tools.

TL;DR: Look in the shop, upgrades, and event menus first; gems in these games usually buy boosts, upgrades, or skips.