From New Babbage Department of Records and Archives
Harbenite. A metal stronger than steel and lighter than cork, used in the production of fanmetal.
Discovery of Harbenite was made by scientist/explorer Erich von Harben, although use of the metal had been going on for generations at the hands of an isolated lake-dwelling tribe in Pellucidarian mountains.
In its natural form, Harbenite ranges from brown to tan to ochre in color, the difference being the density of "harbuncles" in the sample. Harbuncles are crystallized compounds of silica and bauxite arranged naturally around a hollow core, providing a dense but light superstructure. When heated and refined, these harbuncles do not lose their structure, and can be coaxed into closer and closer arrangements, increasing their strength and allowing the matrix in which they bind to be worked. Once refined, harbenite looks and behaves much like steel, but with an ochre tinge. It has no conductive or magnetic properties, and its level of corrosion-resistance increases with its level of refinement.
Harbenite has been used extensively in the construction of girders and structures for airborne vehicles of all kinds. The expense of the refining process means that girders for earthbound structures or naval vessels are possible, though sometimes cost-prohibitive. Harbenite has been used with some success in manufacturing personal body armor, and thick layers have been introduced as reinforcing sections for forts and other defensive emplacements.
(From Tarzan at the Eath's Core, by Edgar Rice Burroughs) Erich von Harben is something of a scientist and explorer himself, and the last time that I saw him he had just returned from a second expedition into the Wiramwazi Mountains, where he told me that he had discovered a lake-dwelling tribe using canoes made of a metal that was apparently as light as cork and stronger than steel. He brought some samples of the metal back with him..."
"...It is not my intention to weary you with a recital of the details of the organization and equipment of the Pellucidarian expedition, although that portion of it which relates to the search for and discovery of the native mine containing the remarkable metal now known as Harbenite, filled as it was with adventure and excitement, is well worth a volume by itself."
"...Exhaustive tests were made of the samples of Harbenite brought to Friedrichshafen by Jason Gridley. Plans were drawn, and by the time the shipment of the ore arrived everything was in readiness to commence immediate construction, which was carried on secretly. And six months later, when the O-220, as it was officially known, was ready to take the air, it was generally considered to be nothing more than a new design of the ordinary type of rigid airship, destined to be used as a common carrier upon one of the already numerous commercial airways of Europe. The great cigar-shaped hull of the O-220 was 997 feet in length and 150 feet in diameter. The interior of the hull was divided into six large, air-tight compartments, three of which, running the full length of the ship, were above the medial line and three below. Inside the hull and running along each side of the ship, between the upper and lower vacuum tanks, were long corridors in which were located the engines, motors and pumps, in addition to supplies of gasoline and oil. The internal location of the engine room was made possible by the elimination of fire risk, which is an ever-present source of danger in airships which depend for their lifting power upon hydrogen gas, as well as to the absolutely fireproof construction of the O-220; every part of which, with the exception of a few cabin fittings and furniture, was of Harbenite, this metal being used throughout except for certain bushings and bearings in motors, generators and propellers.