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Rock on: all about road salt

A specimen of pinkish-red rock salt

Rock salt (halite) from Boulby Potash Mine, North Yorkshire.

© BGS(C)NERC

    • Can you tell what the photo below is? It may not look like it, but it's salt - or rather rock salt!

      Photo showing rock salt which has a look of stuck together mosaic pieces.© BGS, © NERC
      Did you know that it really is salt that goes on our roads in the grit to thaw the ice? But where does it come from?

      Read on as the British Geological Survey (BGS) answers this salty question and more:

      Q: So what is the grit made of that goes on our roads and pavements in winter?
      A: Rock salt is the main ingredient of grit. It is made of the mineral 'halite' (sodium chloride).

      Q: Can you get rock salt in Britain?
      A: Yes - in what's called 'beds' beneath parts of Cheshire, Yorkshire and Northern Ireland. Rock salt is mined at Winsford in Cheshire, Boulby in North Yorkshire and Carrickfergus in Northern Ireland.The UK has large resources of rock salt in the ground which will last for hundreds of years to come.

      You won't find rock salt on the surface - on the ground - because the rain dissolves it.

      Q: What's rock salt used for?

      A: Almost all rock salt mined in the UK is used for road de-icing. Table salt, and salt used as an essential ingredient in products including household bleach and window glass, generally comes from brine (salty water) which is pumped from the salt beds in Cheshire.

      Q: How did the salt come to be deep down underground?
      A: The salt was formed between 300 and 200 million years ago, when much of Britain was covered by a shallow sea surrounded by hot dry desert lands - much like the Persian Gulf today. As the water from this sea evaporated, salt crystals formed from the brine, along with other useful minerals such as gypsum (used for wall plaster) and potash (used for fertiliser).

      Want to know more about rocks?
      You can ask the British Geological Survey a question about geology (the science of the history of the earth as seen in rocks).

      A salty fact
      Did you know some of the books from the Bodleian Library (Oxford University's oldest library), Manchester Library and The National Archives' collections are stored underground in the salt caves? It's so dry down there that the conditions are perfect for the paper in the books!
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