The Liquid Diamond (液体ダイヤ Ekitai Daiya?) is a unique jewel created by a project in Academy City. Akikawa Mie's mother is part of this project, with her father having worked on the vault that was used to hold it.
A liquid diamond is theoretically impossible as diamonds have no melting point. The apparent resolution of this contradiction is what gives value to the liquid diamond. The liquid diamond created by the project however, is actually a condensation of precious metals dissolved in sea water; including gold, platinum, rare earth and carbon, condensed inside a heart or star shaped container. Officially, the liquid diamond is five hundred carats and worth six trillion yen, though Akikawa Mie's mother doubted whether or not one would actually get even a single carat if they gathered it all up, and considered that no one would be buying it anyway. However it is still something rare, never before seen and never having existed before.
The liquid diamond's storage tube has a transmitter attached to it, and even if it were transferred to another container, the creators, having the manufacturing method and patent, would apparently be able to quickly track it down if it were stolen and put on the black market, supposing someone was actually able to sell it off. They are also capable of identifying the specific diamond by checking the plankton in the sea water, so they can retrieve it even via international law.
Magic God Invasion Arc
- Main article: Magic God Invasion Arc
During the High Priest's rampage through Academy City, the vault containing the liquid diamond was compromised. Fearing the damage that would be done to her father, who worked on the vault, and her mother, who worked on the liquid diamond project, if the diamond was stolen, Akikawa Mie took the liquid diamond's storage tube, intending to get it safely to her mother's workplace, escaping from people who wanted the diamond for themselves.
- Shinyaku Toaru Majutsu no Index Light Novel Volume 13 Chapter 2 Part 4
- Shinyaku Toaru Majutsu no Index Light Novel Volume 13 Chapter 2 Part 9