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 diamonds were different. Their colour came from the presence of tiny mineral inclusions. (AUDIO: The Time Capsule)

History[]

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 one parallel universe, Jackie Tyler wore a pair of diamond-studded EarPods, which she was gifted by John Lumic for her birthday. In actuality, these EarPods were used to read her mind. (TV: Rise of the Cybermen ^[+]Error: Code 2 - no data stored in variables, cache or SMW.)

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)

Christina de Souza wore diamond earrings. As she evaded police, she gave them to a bus driver in exchange for a bus ride. (TV: Planet of the Dead ^[+]Russell T Davies and Gareth Roberts, Doctor Who Easter Special 2009 (BBC One, 2009).)

To escape the Last Great Time War, the Time Lords sent a White-Point Star, a form of diamond through the time lock to the Saxon Master. 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 ^[+]Russell T Davies, Doctor Who Christmas Special 2009 and New Year Special 2010 (BBC One, 2009-2010).)

When Vislor Turlough won Enlightenment, he at first believed it to be a huge diamond. (TV: Enlightenment)

Diamonds were common on Telos, where the Cryons offered to pay Lytton and Griffiths in uncut diamonds in return for their services. (TV: Attack of the Cybermen)

Diamonds were among the treasures kept in the Dalek Treasure House on Skaro. (COMIC: Treasure of the Daleks)

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 Bruce Master laid a trap for the Eighth Doctor which resembled a tiny diamond. (PROSE: The Eight Doctors)

The Toymaker had diamonds on the silver collar of his Chinese Mandarin outfit. (PROSE: The Celestial Toymaker)

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 pirates 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 Spiders created giant diamond webs capable of holding asteroids 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)

One planet had diamonds which would disappear if they were carried into the TARDIS. (COMIC: Where Diamonds Are Worthless)