Cut gems are featured throughout the series on jewelry, cutie marks, clothing, and more. Rarity has a particular affinity towards gems: her cutie mark is three lozenge diamonds, and she uses a gem-finding spell in A Dog and Pony Show to get more gems for her gem-studded clothing, the same spell which triggered in The Cutie Mark Chronicles prior to her discovering a rock full of gems. Princess Celestia wears a jewel-studded crown and necklace, and the Elements of Harmony are studded with jewels that match the main ponies' cutie marks. In Sisterhooves Social, Sweetie Belle uses all of Rarity's baby blue sapphires to form the shape of a heart and glues them on a drawing.
Spike's gem-eating diet is first introduced in The Ticket Master where he asks the waiter for rubies. He expresses his love of eating gems in several other episodes, and he's shown eating gems in A Dog and Pony Show, Over a Barrel, Owl's Well That Ends Well, Dragon Quest, Party of One, Secret of My Excess, and Just for Sidekicks. Both the red dragon in Dragonshy and the green dragon in Owl's Well That Ends Well hoard gold and gems in their lairs.In Just for Sidekicks, it is also shown that ponies can and will accept gems as an alternative form of currency in place of bits. Even one tiny, ruby-colored gem was enough for the Cutie Mark Crusaders to purchase a large, industrial-sized pet dryer. In the same episode, Zecora donates a gem to a Girl Scout-like charity. In Rarity Takes Manehattan, Rarity tips a hotel bellhop with gems and insists that he keep the change.
Gems feature prominently in this episode. Rarity runs out of gems for her outfits, and goes searching for them with Spike. She uses a magic spell to locate gems, and Spike digs them out. When they're finished collecting gems, the Diamond Dogs appear and tell Rarity that they "hunt for gems", then kidnap her and force her to find gems for them in their vast underground tunnel system. Spike recruits the other ponies' help, and they eventually find Rarity and leave with several cart-loads of gems, which Spike happily dines on.
After Spike gives Rarity the Fire Ruby, Pinkie Pie tells Spike that Mr. and Mrs. Cake have a "special surprise" for him since it's his birthday. When he enters Sugarcube Corner, the Cakes present him with a blue cupcake studded with sapphires.Alicorn Amulet, a powerful necklace that gave Trixie a lot of magic power. The power of the gem in this episode is used to defeat Twilight in a "Magic Duel." After Twilight finds out Trixie used the Alicorn Amulet to win, she challenges her to another duel using a fake amulet given to her from Zecora, and the help from her friends. After Twilight beats Trixie in the duel, Trixie takes Twilight's fake amulet. Rainbow Dash then takes the Alicorn Amulet and Trixie attempts to attack Rainbow Dash with her magic, but shortly Trixie learns that the amulet that Twilight had was actually a doorstop from Zecora's house. Fluttershy happens to drop by to ask him if he can pet sit Angel, while she and the rest of the Mane 6 are away at the Crystal Empire, and offers a large green gem as payment. Seeing this as the perfect opportunity to replace the ingredients he ate, Spike offers to look after the pets of the others, in exchange for a gem from each owner. However, as his preoccupation with his future jewel cake takes up most of his thoughts, he doesn't take care of the pets as well as he said he would. This irresponsibility causes him to lose his gems one by one as payment for various mishaps, until he only has half of Fluttershy's gem left. He then, ironically, accidently devours it too when he meant to drop it into his cake batter.
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