The best treasure in spell in D&D that generated salt.
There is a retro view of Dungeons & Dragons which suggests the game is mainly about killing things and taking their stuff. This niche has been comfortably filled by video games, which is why modern campaigns tend to put as much focus on the roleplaying and world-building as it does the combat. The current edition of D&D is especially stingy when it comes to magic items. The player is restricted to using three (outside of some basic items, like potions). Gold and jewels are also in short supply, especially in comparison to the D&D campaigns of old.
In the third edition of Dungeons & Dragons, there was a spell that allowed spellcasters to make their own money. The spell was called Wall of Salt and it was found in a book called Sandstorm. Wall of Salt was a fourth level Cleric/Druid/Sorcerer/Wizard spell that did exactly what it said on the tin. A caster summons a wall of salt of an area that was 5ft x the level of the caster. The wall itself was one inch thick, and the spell had no duration and its component was a single salt crystal.
Why D&D's Salt Spell Was So Broken
The reason this spell was so broken can be found on page 112 of the 3.5 Player's Handbook. There is a table that lists the price of trade goods, and a pound of salt is worth the same as a pound of silver. This means every 7th level spellcaster in Dungeons & Dragons could basically cast a spell that prints money. The players could burn all of their spell slots to cast Wall of Salt every day, sell it, and go live on a yacht off the coast of Calimshan.
DMs weren't completely out of options for dealing with the spell. There is nothing in the description for Wall of Salt that claims the salt is edible. It's possible that the spell conjures a white powder which resembles salt, but doesn't actually perform any of the functions of salt. There is also the question of the value of salt. The reason salt is worth as much as silver is because it's rare. If spellcasters suddenly flood the market with salt, then its value will decrease. Not only that, but competitors will spring up in the salt conjuring market.
The fact that Wall of Salt is a divine spell means that Clerics/Druids will have easy access to it, so the players will soon find themselves caught up in a salt production trade war. The history of salt production and how it shaped human civilization is fascinating to read, but it might not make for the most interesting D&D campaign. As such, it might be best for 3.5 DMs to ban this spell from their Dungeons & Dragons table.
