Upsidaisium ore is a naturally occurring mineral found in most parts of the world (curiously, it's absent from the Americas). The ore has a negative weight of about -25 lbs. per cubic foot, though it masses about 200 lbs./cf.

Upsidaisium will rise upwards as if falling until it reaches a height of 12,000 feet (2.27 miles) above sea level (here, it behaves as if it has neutral buoyancy). It seems to be "pushed away" from areas of higher elevation (such that it will never gather around mountain tops or other high places). When left alone, airborne formations tend to gather above low valleys or the open sea.

Upsidaisium ore, sold commercially at ground level, costs $6.25 (£1 5s.) per cubic foot. In the 16th and 17th centuries, earthquakes shook loose some massive deposits in Europe. From the mid-1700s on, about a cubic mile annually (on average) has been lifted from the Earth by natural phenomena.

Careful study has shown that the mineral's weight decreases by ~0.019 carats per cubic foot per year. If this change has always been linear, it means the material was probably deposited around 8 million years ago (and only achieved a negative weight 3 million years ago). A prominent theory suggests that a small moon (perhaps a "wandering planet"), made of a purer form of the mineral, was pushed into Earth's orbit during the late Miocene period.

Upsidaisium ore can be refined into a purer form, but this is quite costly since it requires special equipment and very skilled operators. As the mineral has a very high melting point, it's difficult to achieve relatively high purity (in liquid form, it's prone to rapid oxidization, or bonds too readily with other substances).

Material Cost per cubic inch Cost per cubic foot Weight per cubic inch Weight per cubic foot
Upsidaisium Ore $0.01 $6.25 -0.23 oz. -25 lbs.
30% Pure Upsidaisium $0.02 $19.40 -0.56 oz. -60 lbs.
60% Pure U. $0.04 $59 -1.11 oz. -120 lbs.
90% Pure U. $0.07 $120 -1.67 oz. -180 lbs.
99% Pure U. $0.29 $500 -1.85 oz. -200 lbs.

In some less civilized places, 99% pure Upsidaisium might be used as currency. The advantages would include simple purity tests (just weigh it and compare the volume; something hard to do with gold if people are "diluting" it) and low weight (you could carry a rod with brass fittings to keep it from floating away and the whole assembly could weigh less than an ounce).

A standard form might be a rod of 99% pure Upsidaisium 1 inch thick, 3 inches long, with iron or steel fittings to give it positive weight; such an object would be worth $0.80, though the rod alone would be worth $0.70 if mass-produced. Such a rod would weigh -4.35 ounces, or about a (negative) quarter of a pound.

Upsidaisium refineries or metallurgists' shops would be unusual looking buildings if located above ground (they might be built underground or into the sides of cliffs if working with large pieces). Metallurgists or negative-weight machinists in the city would have large, domed roofs of steel, riveted to iron pillars rooted in a solid concrete foundation.

(All prices on this page are given in 1880s US Dollars/British Pounds.)

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