Crystal chest

The crystal key chest is a treasure chest located in Ivy Sophista's house in Taverley. A second chest is located in Prifddinas in the Iorwerth Clan district. The chests are locked and can only be opened by a crystal key. Attempting to open the chest without the crystal key yields the message: "This chest is securely locked shut." The crystal key is made up of a loop half of a key and a tooth half of a key; you can make the crystal key by using them with each other, or selecting the "Assemble" option.

Opening a crystal chest grants a variety of rewards, which always include an uncut dragonstone. The crystal chest in Prifddinas grants slightly better rewards than the Taverley chest. The crystal key sells for more than most of the rewards, making it more monetarily satisfying to sell the key. When the key is used it disappears, so opening the chest is a gamble.

Rewards
The chest loot always includes an uncut dragonstone, together with a random reward generated from 13 possible reward tables. Below are the values of the chest's contents, based on current Grand Exchange prices.

After an update, wearing a ring of wealth will increase your chances of getting a better drop.

It is only possible to obtain rune platelegs if you are a male character, and a rune plateskirt if you are female character.

It is a common misconception that you can obtain crystal weapons from the chest. The chest does not contain any of these items, as they are a quest reward.

Possibility 1 - Fruit tree seed
The expected value of Possibility 1 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 2 - Lantadyme seeds
The expected value of Possibility 2 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 3 - Grimy torstols
The expected value of Possibility 3 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 4 - Runes
The expected value of Possibility 4 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 5 - Iron ore
The expected value of Possibility 5 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 6 - Coal
The expected value of Possibility 6 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 7 - Rune bars
The expected value of Possibility 7 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 8 - Gems
The expected value of Possibility 8 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 9 - Loop half of a key
The expected value of Possibility 9 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 10 - Tooth half of a key
The expected value of Possibility 10 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 11 - Rune platebody
The expected value of Possibility 11 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 12 - Rune platelegs or plateskirt
The expected value of Possibility 12 is for male characters and  for female characters, which is a profit/loss of  for male characters and  for female characters, if buying the crystal key on the GE.

Possibility 13 - Dragonstone armour
The expected value of Possibility 13 is , which is a profit/loss of if buying the crystal key on the GE.
 * Receiving this possibility is very rare, at a rate of 1/6801. 

Possibilities - Prifddinas chest
This chest was released with the first part of Prifddinas on 22 September 2014, and is located in the Iorwerth Manor against the south wall. It has an improved drop table over the chest in Taverley. While the Voice of Seren is active for the Iorwerth clan, the chest provides an increased chance of Prifddinas-related items looted, including: corrupted ore, Crystal tree blossoms, and Crystal motherlode shards. At the least, the player should still wear a Ring of wealth when opening either crystal chest.

Possibility 1
The expected value of Possibility 1 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 3 - Tooth half of a key
The expected value of Possibility 3 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 4 - Loop half of a key
The expected value of Possibility 4 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 6 - Ores
The expected value of Possibility 6 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 7 - Rune Halberd
The expected value of Possibility 7 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 8 - Rune armour
The expected value of Possibility 8 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 9 - Rune platelegs or plateskirt
The expected value of Possibility 9 is for male characters and  for female characters, which is a profit/loss of  for male characters and  for female characters, if buying the crystal key on the GE.

Possibility 10 - Rune bars
The expected value of Possibility 10 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 11 - Talismans
The expected value of Possibility 11 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 12 - Uncut gems
The expected value of Possibility 12 is , which is a profit/loss of if buying the crystal key on the GE.

Possibility 13 - Dragonstone armour
The expected value of Possibility 13 is , which is a profit/loss of if buying the crystal key on the GE.
 * Receiving this possibility is very rare, at a rate of 1/6801. 

Probabilities - Taverley chest

 * The probabilities in this section are an estimation based on the data of 1134 crystal chest loots on the Taverley chest, while wearing a ring of wealth.

Using these probabilities, the expected average profit/loss, per crystal key, when looting the crystal chest is. (Assuming you will receive whichever of the rune platelegs and rune plateskirt is worth more, and the crystal key is bought at GE price). This is excluding the possibility of receiving a dragonstone armour piece, as this possibility is much too rare to estimate with any acceptable accuracy.

Trivia

 * The crystal key chest was reworked on 11 June 2013 with the release of the Triskelion Treasures. Previous old drops, such as receiving 2,000 coins and a Spinach roll along with an Uncut dragonstone, were removed, and new ones were added, such as the Dragonstone armour.

Crystal chestCrystal chest