Diamond Diamonds were a form of crystallised carbon and one of the most valuable substances in the universe . Only one of every 10 . 000 diamonds that were minded on Earth were coloured . Most of these got their colour from chemical impurities or defects in the stone itself . However black diamond s were different . Their colour came from the presence of tiny mineral inclusions . ( AUDIO : " The Time Capsule " ) Planet One , the first planet in the universe , had a cliff made of pure diamond . ( TV : " The Pandorica Opens " ) In 1879 , the Tenth Doctor used the infamous Koh - i - Noor diamond to kill a werewolf by using it to reflect enough moonlight from the light chamber to be fatal to it . ( TV : " Tooth and Claw " ) Around the turn of the 20th century , the Fourth Doctor used a diamond as a focusing piece to turn Fang Rock lighthouse into a carbon oscillator . He obtained the diamonds from Henry Palmerdale , who carried them as a secure currency , and used the laser to destroy a Rutan mothership . ( TV : " Horror of Fang Rock " ) In 1909 , while working for an unknown employer , Jack Harkness stole diamonds from a mine in Lahore . ( TV : " Small Worlds " ) In 2009 , members of the Slitheen family attempted to compress the planet Earth into a diamond , but were stopped by members of the Slitheen - Blathereen family . ( TV : " The Gift " ) To escape the Last Great Time War , the Time Lord s sent a White - Point Star , a form of diamond through the time lock to . He used it to amplify the signal and bring them to Earth , but the Tenth Doctor shot it with Wilfred Mott ' s old service revolver , destroying it and the link . ( TV : " The End of Time " ) When Vislor Turlough won Enlightenment , he at first believed it to be a huge diamond . ( TV : " Enlightenment " ) Diamonds were common on Telos , where the Cryon s offered to pay Lytton and Griffiths in uncut diamonds in return for their services . ( TV : " Attack of the Cybermen " ) The planet Midnight ' s surface was mostly diamonds , but since the planet went through harsh X - tonic radiation , the diamonds could not be excavated . ( TV : " Midnight " ) In the 40th century , Baltazar attempted to compress the planet Earth into a diamond , but was stopped by the Tenth Doctor and Martha Jones . ( TV : " The Infinite Quest " ) The diamond mines of Barzilla were abandoned by the time Sara Kingdom visited that planet . ( PROSE : " The Outlaw Planet " ) The planet Sartor was rich in diamonds , which were mined by the human colonists . Quarsian pirate s attempted to steal the diamonds , but were defeated by the Tenth Doctor . ( COMIC : " The Diamonds of Sartor " / " Quarsian Mission " / " Android of Death " ) In the distant future , one of the Three Great Treasures of Generios was the largest diamond in existence , which was guarded by a Jelloid . ( AUDIO : " The One Doctor " ) At the end of the universe , it was believed that the skies of Utopia were made of diamonds . ( TV : " Utopia " ) Diamond Spider s created giant diamond webs capable of holding asteroid s in place . ( PROSE : " Web in Space ! " ) The star - liner " Excelsis " was powered by zero - point energy focused through the Eye of Ashaya , the largest diamond in the galaxy . ( COMIC : " The Eye of Ashaya " ) Azbantium was 400 times harder than diamond . ( TV : " Heaven Sent " ) The Halassi Androvar was the most expensive diamond in the galaxy in 5343 . ( TV : " The Husbands of River Song " )