d66/d18 Gems and their Magical Properties

[Edit 21/06/2021 to replace old table & add pic]

All gems are worth their base value (1 to 18, below) in the common currency unit of my/your setting, multiplied by d6 x 10 or 10d6 (if you prefer).

They are either the size they would be in reality, or they are about the size, shape and colour of the dice you are holding at the time. Or compare them to bird's eggs, quail up to duck.

Gems can be kept as treasure (to be traded for cash and counted towards XP after an adventure) or can be used during an adventure as a one-shot magic item.

Once used, gems shatter, disintegrate or are otherwise destroyed; the remnants are worthless.

If you intend to save a gem to use in a future episode/session of your current adventure, it cannot be counted towards experience even if you later change your mind and trade it for cash (you still get the money). Define the boundaries/unit of 'an adventure' if your game does not already cover this.

You cannot buy gems on the open market to take them into an adventure to use as magic items under normal circumstances. Their magical powers are a property of the condition of 'adventure' and as such do not operate outside of this - they are drained by exposure to the mundane.

Ignore any of this that doesn't fit with the game you want to play.

Roll 2d6:

1st d6 (1 to 2) 2nd d6:

1. Quartz (1): reroll 1s on any roll, once.
2. Lapis Lazuli (2): reroll a failed fear/ morale save.
3. Topaz (3): reroll a failed spell save.
4. Coral (4): cure wounds at 0 hp.
5. Turquoise (5): reroll or force a Reaction Roll.
6. Amethyst (6): reroll a failed Strength roll.

1st d6 (3 to 4) 2nd d6:

1. Amber (7): reroll a failed Constitution roll.
2. Carnelian (8): reroll a failed warding, spell casting or attack (melee or missile) roll.
3. Opal (9): reroll a failed Intelligence or Wisdom roll.
4. Jacinth (10): reroll fire damage or failed fire save.
5. Aquamarine (11): cure wounds or doubles effect of your casting.
6. Jade (12): reroll a failed Dexterity or Charisma roll, or a failed missile attack roll (thrown or device).

1st d6 (5 to 6) 2nd d6:

1. Serpentine (13): reroll a failed attempt to deceive/ stealth/ steal/ backstab.
2. Pearl (14): reroll a failed polymorph/ petrification save.
3. Ruby (15): reverse a failed roll, automatically succeed on a roll, or convert a success to a best possible result.
4. Sapphire (16): recover a cast spell without penalty.
5. Diamond (17): protection from damage, or reroll a death save.
6. Emerald (18): protection from/ dispel magic.

This table is based on the Gem Generator from the UK Corgi paperback edition of Tunnels & Trolls, which is where I first encountered the d66 table.