The Amethyst was a rare pin in Club Penguin. All players could obtain it by digging up four pieces of it from the dirt pit in the Cave Mine during the Cave Expedition, by dancing with either a Hard Hat or a Snow Shovel. After several seconds of "digging" in one spot, the player would receive one of the four pieces of the pin, with a popup notifying of this each time.
Obtaining this pin was required to access the Hidden Lake during the expedition, as a boulder blocked the tunnel to it until this pin was obtained. Once the Hidden Lake reopened in March 2010, this pin was no longer required to access it.
The functionality of digging for pieces of this pin in the Cave Mine's pit returned after the room reopened in March 2010, but coins were dug up instead. After the Cave Mine closed in November 2013, this function was moved to the Gold Mine.