Philosopher's stone

A philosopher's stone was a rare magical substance and artifact reputed to have the power to transmute base metals into precious metals, cure diseases, and even bring the dead back to life. They could be used by any wielder of arcane magic, particularly alchemists.

Description
Two main types of philosopher's stone have been reported.

A philosopher's stone was originally said to appear exactly like a luckstone or loadstone. In fact, discerning a philosopher's stone from a luckstone seemed to require some destructive testing: placing a suspect stone in molten lead would destroy a luckstone, but not a philosopher's stone. It was impervious to heat; even dragon-fire would not melt it.

Alternatively, after the, a philosopher's stone was described as an ordinary-seeming hunk of sooty, blackish rock, weighing around. At its core was a cavity lined with magical mercury, which was the operative part of the philosopher's stone. However, the stone had to be broken open to access it, after which it became unstable and lost its power within the day.

In any case, philosopher's stones could vary widely in quality and effectiveness.

Powers
The original type of philosopher's stone had anywhere up to eight charges, with a minimum of two. An alchemist could use one charge to boost their research abilities or else to transmute of lead into silver or gold (with a one-in-two chance). Provided one charge remained, an alchemist could not contract a disease while they possessed the stone on them, and could even cure disease once a day, without a charge being lost. But when the last charge was used, the stone disintegrated. The glorious transmutation spell, of which only the mightiest mages were capable, used a philosopher's stone to transmute a greater mass of metal as the caster chose: 50‒500 pounds (23‒230 kilograms) of iron to silver or 10‒100 pounds (4.5‒45 kilograms) of lead to gold. The stone was destroyed in the process.

In the second type, an arcane spellcaster could use the magical mercury of one philosopher's stone to transmute of lead into gold, or  of iron into silver. Alternatively, the mercury could be mixed with any cure wounds potion to create a unique "oil of life" that, if sprinkled upon a corpse, would resurrect the deceased.

Creation
According to no less a sage than Elminster, it was possible to make a philosopher's stone, but the process was quite complex and involved. It was known that, first, a mage or alchemist must discover (perhaps through adventuring) the correct alchemical formula, including the required ingredients and their method of preparation. The resulting mixture then needed to be enchanted with the enchant an item spell, and then subject to the special, high-powered spell known as hatch the stone from the egg (this was not the same as the alchemical formula). With this, the mixture was slowly transmuted into a philosopher's stone. The final step was to make this last with a permanency.

One item needed was the magical glass retort known as a philosopher's egg, which aided in the making of mundane and magical liquids. It was because of this that mages said that "the stone hatches from the egg". It was itself the material component for hatch the stone from the egg, but was not destroyed in the process. It held the alchemical mixture that would become the philosopher's stone.

Rumor held that a king's tear was also somehow linked to the process, and to the creation of other magical items.

History
Circa 1357 DR, vast tracts of land in the Hills of Maerth in Chessenta were bought up by the famed archmage and planewalker Azurax Silverhawk, who was searching for a philosopher's stone.

In the mid–14 century DR, after Khenel Barony, the business-wizard of Waterdeep, learned a local thieves' guild had come into possession of a philosopher's egg, he orchestrated a takeover of the organization. He intended to use the egg to craft a philosopher's stone in order that he might "revitalize the economy", making himself extremely wealthy in the process.