Phlogistonite

Phlogistonite is a rare substance, first discovered by Percival Lowell. Its explosive properties are of such immense power that sufficient quantities of it are capable of launching a train-sized bullet outside of the Earth's gravitational field, which made it an ideal fuel for powering Lowell's manned space cannon.

History
During the events of Martian Dreams, Lowell and numerous luminaries of the Victorian era were propelled to Mars on a phlogistonite-powered space capsule, after the Russian monk, Grigori Rasputin, sabotaged the launch by igniting the cannon's fuse prematurely. Two years later, a rescue mission manned by Nikola Tesla used similar technology to send a second crew to the red planet. The Avatar was among these travelers, having arrived along with Dr. Spector in the year 1895 via an orange-hued time gate.

Once numerous issues involving the bygone native Martians and the logistics of powering their alien equipment had been addressed, Andrew Carnegie was able to construct a space cannon for the return journey home. Unfortunately, the phlogistonite fuel canisters which had been transported to the planet were stolen by Rasputin, who had long been under the influence of the malevolent Martian, Raxachk. After deducing this with the assistance of Theodore Roosevelt, the Avatar's company confronted Raxachk in Argyre, whereupon the villain boasted of having perfected a way to move material objects into the Martians' metaphysical "Dream-World" and indicated that the phlogistonite had been transported there.

Faced with the possibility of sparking a cataclysm of epic proportions, by removing the phlogistonite from such a plane, the Avatar endeavored to secure the survival of the remaining Martians (all trapped in the Dream-World following the death of their bodies), before attempting to collect the fuel. The hero was eventually able to enact a means of transferring the consciousnesses of Martian people into humanoid automatons, and gave instructions to Jack Segal as to how to complete this process while the Avatar dealt with the problem of Raxachk and the phlogistonite.

Abandoning Rasputin's body, the rogue Martian had fled into the Dream-World where the fuel lay in storage. The Avatar used the Martian Dream Machine to seek out Raxachk and, after a final confrontation, was able to safely retrieve the phlogistonite canisters, enabling the transport of humans and Martians alike back to Earth.

Trivia

 * The term phlogistonite is likely derived from the now defunct phlogiston theory of the seventeenth century, which held that all flammable materials contained an odorless, colorless, tasteless compound without mass which was known as phlogiston. Phlogiston was theoretically liberated from substances by burning. (The eventual "dephlogisticated" form of the substance was known as the calx.) It seems feasible that the fictional phlogistonite could be a theoretical mass made entirely of phlogiston, explaining its immense explosive power.