Many people here have likely played Spore, a game where you design a species and expand its empire into space and beyond. It was one of those games that worldbuilders absolutely adored and after recently playing it I noticed something that could be interesting to see in my world. Spice Geysers;
To people who have not played the game, these geysers produce spice which acts as currency. What I'm wondering is, could these Spice Geysers exist in a realistic way?
My first thought, probably triggered by "spore", is to make them the vents of underground possibly burrowing fungal life forms. Something like the puffball mushroom family but giant sized.
They could periodically vent to spread their spores.
If these spores had a useful property (my first thought is hallucinogenic drug) then they could easily be used as a trade good or currency.
The closest Real life example I can give you for a spice geyser is any geyser that contains salt water. This isn't exactly a "spice" geyser as salt isn't technically a spice (its a seasoning). In addition, it would require a lot of refinement to get the salt ready for use. However, it would likely require about the same refinement as any other source of salt derived from salt water. As far as use for currency, salt was used as a currency and highly valued commodity for many years, but that might not be exactly what you are looking for.
When I think of spice as a currency, one thing jumps directly mind. This is the spice Melange, from the classic novel Dune. Dune is a seminal sci-fi book, and should be instantly recognizable to any fan of fictional literature. The book revolves around conflict over the spice Melange. Melange grants a great many boons to its users (as a drug) and can be found on only one planet, Arrakis. Spice almost certainly acts as currency in Dune, and is highly coveted by all, to the point where it is said that a one briefcase full of spice would be enough to purchase an entire planet. More specific to your "Spice Geysers", there is a phenomenon in the dune universe called a spice blow that would appear to observers much like a geyser.
@superluminary 's answer is actually somewhat related to mine. The Author of Dune, Frank Herbert explicitly identified CHOAM with OPEC, equating the spice melange to oil in an interview with OMNI magazine.
Edit: Artist's Rendering of a Spice Blow
The definition of a spice is:
an aromatic or pungent vegetable substance used to flavour food, e.g. cloves, pepper, or cumin.
It is a biological material, that can be used to impart flavour to food.
So we might ask, what biological material do we see gushing out of the ground in our world? One solution might be oil.
On Earth, the ultimate breakdown product of sea animals and plants is crude oil and natural gas. Crude oil is a complicated cocktail of hydrocarbons, which can be refined into petrol, diesel, lubricating oil, and other carbon-based substances.
Imagine if the breakdown product of dead sea life were palatable. Wine and Cheese improve with age (up to a point). The Chinese eat "100-year-old eggs".
We can then postulate a planet with spice pools instead of tar pits, and spice gushers instead of oil.
If you replace "spice" with any valuable material, simply for the fact that those are needed for something and it's easier to extract from natural occuring geysers than importing them from other worlds... Check for eruptions on Io (sulfur, an important component for metabollism of anything organic, and you can also make some salts with that) and Triton (nitrogen, you can make laughing gas or an Earth-like atmosphere for a ship with enough of that) (also actual geysers, more tame than Io's volcanoes).
In fact, thinking back about Io... If that sulfur is bound to any metal in any form, it should taste salty, maybe spicy... For the very definition I know for a chemical salt is the ionic binding between a metal and a non-metal. I don't recommend trying any of those salts in your diet, though.
There are bacteria that live near volcano and deep sea vents that feed off the heat similar to how surface plants feed off of light. Geysers are just hot springs that build up pressure. It's potentially possible that some deep-sea-vent bacteria that produced some desirable spice could adapt to living near geysers. Then their produced spices could seep into the ground (and thus into the water of the geyser), and the spice is harvested from water rather than risking damaging the ground the bacteria are in.
