Gem Rummy is similar to standard Gin Rummy except each card has a background color & gem symbol; Kings have two background colors; (Jokers are included but are not used in hands). Adding colors to each card allows for more interesting combinations (like having all eight gems in hand). Another difference is that (2) 6-sided dice are used at the beginning of each hand to establish the "Knock number", and also the "Diamond number" for a special meld called "Queen's Diamonds".
The object is to get your hand down to a few points of Deadwood by getting Melds.
There are 3 phases to each hand: 1) DEAL & ROLL; 2) CARD PLAY; 3) SHOWDOWN & SCORING.
Cards in Melds and Lay-offs will not score for your opponent, but have no inherent point values themselves. Cards not in Melds or Lay-offs are called Deadwood and might add points to your opponent’s score.
There are 4 different Melds available: Sets, Runs, Stashes, and Queen’s Diamonds (the latter two are new).
SET: At least 3 cards of the same rank (i.e., 5, 5, 5).
RUN: At least 3 consecutive cards in the same suit (i.e., 6, 7, 8, all clubs).
STASH: At least 4 cards of the same gem color (i.e., 4 Emeralds).
QUEEN’S DIAMONDS: Any Queen + one designated Diamond card that is determined by the initial roll number on the dice. Both dice are rolled to find one number (i.e., 3 and 4 = 7, indicating 7 of Diamonds is the card). An “11” or “12” indicates JACK of DIAMONDS.
Also, "Gem Parts" is a bonus players can earn by having all 8 gems at the end of a hand.
A new minimum score rule keeps the game moving along nicely.
—description from the designer