Sylvite
Potassium chloride, laid down where ancient seas dried out — the mineral that is potash, and the potassium in fertiliser.
Sylvite is potassium chloride and looks very like halite, with which it is almost always found. It forms in the same way — an evaporating sea — but later in the sequence, because potassium salts stay in solution longer than sodium ones and only crystallise once the brine is nearly gone.
That makes sylvite rarer and more valuable than rock salt, and it is essentially the world's only source of potassium for agriculture. Plants need potassium in quantity, soils lose it to cropping, and there is no synthetic substitute — it must be mined.
How to identify it
Sylvite is distinguished from halite by taste — distinctly bitter where halite is simply salty — and by being slightly softer and less dense. Both are cubic with perfect cubic cleavage and both are commonly colourless to reddish from included iron oxide.
Economic significance
Potash deposits are concentrated in very few countries, which makes fertiliser potassium one of the more geographically constrained commodities in the food system — comparable to phosphate, and unlike nitrogen, which can be fixed from the air anywhere there is energy.
Disruption to potash supply therefore transmits to crop yields with a lag of a season or two, and the mineral's distribution is a live question in agricultural policy rather than a geological footnote.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
is an ore of
- Potassium — element · essentially the world's only source of agricultural potassium Wikidata
is commonly confused with
- Halite — mineral · cubic, colourless and found together; sylvite tastes bitter where halite is simply salty
is a component of
- Evaporite — rock · one of the last salts to precipitate, needing near-total desiccation — which is why potash deposits are far rarer than salt ones
Sources
- Material WorldOur own writing
- Wikimedia Foundation · Creative Commons CC0 1.0 Universal (public domain dedication)
- COD Advisory Board / Vilnius University · CC0 — contributors place data in the public domain