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Release date  22 September 2014 (Update) 

Members  Yes 
Quest  Plague's End 
Location  Prifddinas 
Examine  A crystal key can open it. 
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 generally more profitable to sell the key than to use it. The key is used once and disappears upon usage.
Rewards possibilities
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. Unless otherwise specified, all possibilities give all of the listed rewards when obtained.
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 a female character.
Taverley chest
Possibility 1  Fruit tree seed
The expected value of Possibility 1 is 17,139, which is a profit/loss of −4,672 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Calquat tree seed  1  Common^{[1]}  321  
Papaya tree seed  1  Common^{[1]}  2,896  
Palm tree seed  1  Uncommon^{[1]}  39,600 
Possibility 2  Lantadyme seeds
The expected value of Possibility 2 is 13,529, which is a profit/loss of −8,282 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Lantadyme seed  2  Common  1,452 
Possibility 3  Grimy torstols
The expected value of Possibility 3 is 22,855, which is a profit/loss of 1,044 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Grimy torstol  2  Common  10,778 
Possibility 4  Runes
The expected value of Possibility 4 is 172,427, which is a profit/loss of 150,616 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Law rune  50  Common  28,500  
Chaos rune  50  Common  7,600  
Cosmic rune  50  Common  20,600  
Death rune  50  Common  11,600  
Nature rune  50  Common  20,250  
Body rune  200  Common  9,600  
Mind rune  200  Common  3,800  
Earth rune  200  Common  3,600  
Air rune  200  Common  18,000  
Water rune  200  Common  5,000  
Fire rune  200  Common  31,800 
Possibility 5  Iron ore
The expected value of Possibility 5 is 101,877, which is a profit/loss of 80,066 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Iron ore  200 (noted)  Common  89,800 
Possibility 6  Coal
The expected value of Possibility 6 is 28,877, which is a profit/loss of 7,066 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Coal  150 (noted)  Common  16,800 
Possibility 7  Rune bars
The expected value of Possibility 7 is 21,032, which is a profit/loss of −779 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune bar  3  Common  8,955 
Possibility 8  Gems
The expected value of Possibility 8 is 32,132, which is a profit/loss of 10,321 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Uncut diamond  3  Common  14,529  
Uncut ruby  3  Common  5,526 
Possibility 9  Loop half of a key
The expected value of Possibility 9 is 38,130, which is a profit/loss of 16,319 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Loop half of a key  1  Common  11,053  
Coins  15,000  Common  15,000 
Possibility 10  Tooth half of a key
The expected value of Possibility 10 is 38,615, which is a profit/loss of 16,804 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Tooth half of a key  1  Common  11,538  
Coins  15,000  Common  15,000 
Possibility 11  Rune platebody
The expected value of Possibility 11 is 49,557, which is a profit/loss of 27,746 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune platebody  1  Common  37,480 
Possibility 12  Rune platelegs or plateskirt
The expected value of Possibility 12 is 49,079 for male characters and 49,138 for female characters, which is a profit/loss of 27,268 for male characters and 27,327 for female characters, if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune platelegs  1  Common^{[1]}  37,002  
Rune plateskirt  1  Common^{[1]}  37,061 
Possibility 13  Dragonstone armour
The expected value of Possibility 13 is 7,292,370, which is a profit/loss of 7,270,559 if buying the crystal key on the GE.
 Receiving this possibility is very rare, at a rate of 1/6801.^{[1]}
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Dragonstone helm  1  Very rare^{[2]}  7,341,200  
Dragonstone hauberk  1  Very rare^{[2]}  12,743,872  
Dragonstone greaves  1  Very rare^{[2]}  6,133,880  
Dragonstone gauntlets  1  Very rare^{[2]}  5,932,094  
Dragonstone boots  1  Very rare^{[2]}  4,250,417 
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. At the least, the player should still wear a Ring of wealth when opening either crystal chest.
Possibility 1  Tree seeds
The expected value of Possibility 1 is 55,516.6, which is a profit/loss of 33,705.6 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Yew seed  1  Common  15,302  
Papaya tree seed  1  Common  2,896  
Elder seed  1  Uncommon  180,802 
Possibility 2  Herb seeds
The expected value of Possibility 2 is 13,979, which is a profit/loss of −7,832 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Dwarf weed seed  1  Common  822  
Torstol seed  2  Common  1,080 
Possibility 3
The expected value of Possibility 3 is 49,832, which is a profit/loss of 28,021 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Grimy lantadyme  5  Common  37,755  
Crystal tree blossom  1  Common  Not sold 
Possibility 4  Talismans
The expected value of Possibility 4 is 18,178, which is a profit/loss of −3,633 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Fire talisman  5 (noted)  Common  1,045  
Water talisman  2 (noted)  Common  5,056 
Possibility 5  Rune Halberd
The expected value of Possibility 5 is 21,455, which is a profit/loss of −356 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune halberd  1  Common  9,378 
Possibility 6  Ores
The expected value of Possibility 6 is 23,307, which is a profit/loss of 1,496 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Coal  80 (noted)  Common  8,960  
Adamantite ore  10 (noted)  Common  2,270  
Corrupted ore  50  Common  Not sold 
Possibility 7  Rune bars
The expected value of Possibility 7 is 21,032, which is a profit/loss of −779 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune bar  3  Common  8,955 
Possibility 8  Uncut gems
The expected value of Possibility 8 is 32,132, which is a profit/loss of 10,321 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Uncut diamond  3  Common  14,529  
Uncut ruby  3  Common  5,526 
Possibility 9  Loop half of a key
The expected value of Possibility 9 is 23,130, which is a profit/loss of 1,319 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Loop half of a key  1  Common  11,053  
Crystal motherlode shard  10  Common  Not sold 
Possibility 10  Tooth half of a key
The expected value of Possibility 10 is 23,615, which is a profit/loss of 1,804 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Tooth half of a key  1  Common  11,538  
Crystal motherlode shard  10  Common  Not sold 
Possibility 11  Rune armour
The expected value of Possibility 11 is 63,619, which is a profit/loss of 41,808 if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune full helm  1  Common  20,892  
Rune kiteshield  1  Common  30,650 
Possibility 12  Rune platelegs or plateskirt
The expected value of Possibility 12 is 49,079 for male characters and 49,138 for female characters, which is a profit/loss of 27,268 for male characters and 27,327 for female characters, if buying the crystal key on the GE.
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Rune platelegs  1  Common^{[1]}  37,002  
Rune plateskirt  1  Common^{[1]}  37,061 
Possibility 13  Dragonstone armour
The expected value of Possibility 13 is 7,292,370, which is a profit/loss of 7,270,559 if buying the crystal key on the GE.
 Receiving this possibility is very rare, at a rate of 1/6801.^{[1]}
Item  Quantity  Rarity  GE price  

Uncut dragonstone  1  Always  12,077  
Dragonstone helm  1  Very rare^{[2]}  7,341,200  
Dragonstone hauberk  1  Very rare^{[2]}  12,743,872  
Dragonstone greaves  1  Very rare^{[2]}  6,133,880  
Dragonstone gauntlets  1  Very rare^{[2]}  5,932,094  
Dragonstone boots  1  Very rare^{[2]}  4,250,417 
Probabilities
Taverley chest
 The probabilities in this section are an estimation based on the data of 1000 crystal chest loots on the Taverley chest, while wearing a luck of the dwarves.
Possibility  Percentage 

Possibility 1: Fruit tree seed  6.4%^{[notes 1]} 
Possibility 2: Lantadyme seeds  7.9% 
Possibility 3: Grimy torstols  9.4% 
Possibility 4: Runes  10% 
Possibility 5: Iron ore  9.1% 
Possibility 6: Coal  9.8% 
Possibility 7: Rune bars  9.4% 
Possibility 8: Gems  8.3% 
Possibility 9: Loop half of a key  7.4% 
Possibility 10: Tooth half of a key  6.8% 
Possibility 11: Rune platebody  7.2% 
Possibility 12: Rune platelegs or plateskirt  8.3% 
Possibility 13: Dragonstone armour  < 0.01% 
 ^ The official RuneScape wiki lists the probability of receiving a calquat or papaya tree seed at 5:11 (45.45%) each and the probability of receiving a palm tree seed at 1:11 (9%). This data shows a probability of 48.45% for the calquat, 42.18% for the papaya, and 9.37% for the palm tree seed.
Using these probabilities, the expected average profit/loss, per crystal key, when looting the crystal chest is 29,584. 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.
Prifddinas chest
 The probabilities in this section are an estimation based on the data of 20,000 loots of the Prifddinas crystal chest while wearing luck of the dwarves. The loot from the Prifddinas chest is not affected by the Voice of Seren.^{[1]}
Possibility  Percentage 

Possibility 1: Tree seeds  7.59% 
Possibility 2: Herb seeds  7.555% 
Possibility 3: Grimy lantadymes  4.47% 
Possibility 4: Talismans  7.545% 
Possibility 5: Rune Halberd  6.00% 
Possibility 6: Ores  10.36% 
Possibility 7: Rune bars  9.455% 
Possibility 8: Gems  9.525% 
Possibility 9: Loop half of a key  9.30% 
Possibility 10: Tooth half of a key  9.045% 
Possibility 11: Rune full helm and rune kiteshield  8.81% 
Possibility 12: Rune platelegs or plateskirt  10.34% 
Possibility 13: Dragonstone armour  < 0.01% 
Using these probabilities, the expected average profit/loss, per crystal key, when looting the crystal chest is 10,782. Assuming you will receive rune platelegs, the crystal key is bought at GE price and the luck of the dwarves ring is worn. This is excluding the possibility of receiving a dragonstone armour piece, as this possibility is much too rare to estimate with any acceptable accuracy.
Estimate probabilities for nonguaranteed loot are:
 17.785% chance of crystal motherlode shard when rolling possibility 9 or 10. This assumes that possibility 9 and 10 yield the same chance for crystal motherlode shards.
 8.675% chance of receiving elder seed when rolling possibility 1.
 63.385% chance of receiving papaya tree seed when rolling possibility 1.
 27.94% chance of receiving yew seed when rolling possibility 1.
 20.39% chance of receiving dwarf weed seed when rolling possibility 2.
 79.61% chance of receiving torstol seed when rolling possibility 2.
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.
 The estimated dragonstone armour possibility chance is about 0.000147%.
References
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