Gelatin Crystal

The Gelatin Crystal is a consumable item used to summon the Queen Slime boss. It can be found on Pearlstone or Pink Ice Blocks in the Underground Hallow. Upon breaking it, it drops the item used to summon the Queen Slime. It can be used at any time of day, and any depth as long as the player is in the Hallow. Similar to farming Crystal Shards, Gelatin Crystals can be quickly farmed by placing rows of Pearlstone Blocks / Pink Ice Blocks in straight lines in the Underground Hallow.

Trivia

 * Unlike another naturally spawning boss summoning item (Plantera's Bulb), Gelatin Crystals do not require a minimum distance between each other to generate which can lead to two or more of them generating very close together.
 * The Gelatin Crystal will be identified as a Crystal Shard by the Minimap, even though it is not.