Metallic, silver-gray cubic crystal
|Behind the Scenes|
Unobtanium (pronounced un-ob-tain-ee-um) is a highly valuable mineral found on the moon Pandora. Humans mined unobtanium for energy generation, as the RDA was suppressing the development of alternatives on Earth. The value and mining process of the mineral was the primary cause for the poor state of human and Na'vi relations, only worsening as the years progressed.
It is a room-temperature superconductor for energy, which makes it very valuable; worth $20 million per kilogram (2.2 lbs) unrefined and $40 million per kilogram refined on Earth. However, as the Pandoran atmosphere is toxic to humans, it is expensive to mine. For mining operations, all human personnel are required to wear an exopack in order to breathe while working. Humans transport unobtanium on trucks called Hell Trucks from the mining sites back to Hell's Gate for refining and eventual transport to Earth.
Unobtanium proved to be the most baffling of scientific discoveries in the area of superconductors as it had an extremely strong magnetic field, reversing prior knowledge that all superconductors repel magnetic fields. Furthermore, unlike the fragile crystals of human-created superconducting compounds, the substance found on Pandora was a stable quasi-crystal with its atoms arranged in a never-repeating but orderly pattern with fivefold symmetry. This matrix was not only structurally rugged but also housed microscopic voids in the quasicrystalline structure that contain the magnetic flux lines (see Type II superconductor). These unusual properties cause the mineral to levitate in magnetic fields, under the Meissner Effect.
On Pandora, the magnetic effect is exemplified in huge outcroppings of unobtanium ripping loose from the surface and floating in magnetic vortexes. These huge "islands", named the Hallelujah Mountains by Earth's explorers, are called Thundering Rocks by the Na'vi, who hold them sacred. The unique magnetic properties of unobtanium are used to contain and direct the energy of the matter-antimatter annihilation which propels ships like the ISV Venture Star.
Without unobtanium, interstellar commerce on such a scale would not be possible. Unobtanium is not only the key to Earth’s energy needs in the 22nd century, but the enabler of interstellar travel and establishment of a truly spacefaring civilization. This creates a feedback loop: The more unobtanium is mined, the more ships can be built and the more equipment can be sent to Pandora for further mining.
Originally, the term, "unobtanium" was slang used in the aerospace industry, to describe hard-to-access materials with mythical properties. However, over the years the name appears to have stuck. 
Researchers theorize that billions of years ago, when the planets and satellites of the Alpha Centauri System were condensing from the primordial stellar nebula, a Mars-sized stellar body may have crashed into the still-molten Pandora. The moon's nickel-iron core was disrupted. The high temperatures and pressures produced far exceeded anything wrought by human technology. These forces interacted with Polyphemus' intense magnetic field and created conditions suitable for the formation of unobtanium.
Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at temperatures close to absolute zero; it proved to be useless because of the logistics of cooling large amounts of material down that far. Further efforts proved futile, and frustrated researchers finally termed their goal "unobtainium." (The spelling was later changed to "unobtanium" to conform to the chemical element naming, even though unobtanium is a compound, not an element.) There matters stood until the first unmanned exploration vehicle reached Alpha Centauri System and discovered deposits of a room temperature superconducting substance on an Earth-like moon named Pandora—unobtanium had been obtained at last.
- A similar material or compound appeared in the Terminator franchise, also by James Cameron. Simply referenced as the "room-temperature superconductor", it caused a nuclear holocaust after it was used to create the first sentient computer, Skynet.
- The name "unobtanium" is an old engineering joke, and can be applied to any rare or hard to find material that has the properties needed to fulfil a given design, but is unobtainable. 
- This joke became a trope in science fiction: any material that is extremely useful (often crucial for all fictional technology), hard to find and is thus practically unobtainable is collectively described as unobtanium.
- The mineral shown as "unobtanium" in reality is called galena, and is the chief ore of the actual element lead. It is a very dense rock made of lead sulfide.
- In the Activist Survival Guide, unobtanium is listed incorrectly as element 120 in an image spread, even though it was stated that unobtanium is a compound, not an element, just two pages prior. The actual element 120, given the temporary name Ununennium (1-2-0 in Latin), has not yet been synthesised.
- The plant Sol's Delight is magnetropic, and orients itself towards magnetic fields. Miners were able to use this trait to locate unobtanium deposits.
- In the Pandorapedia in James Cameron's Avatar: The Game, the price is erroneously listed as 20 billion dollars rather than 20 million.
- James Cameron's Avatar: An Activist Survival Guide, page 18
- AVATAR Scriptment, page 13.
- James Cameron's Avatar: An Activist Survival Guide, page 17
- See Wikipedia's article for more information.
- See Wikipedia's article for more information.
- James Cameron's Avatar: An Activist Survival Guide page 19