Rock salt 'grit' is vital for keeping our road traffic moving in icy weather.
What is it made of?
Where does it come from?
How much is there in the UK?
Rock salt is the key ingredient in the 'grit' which keeps our road network moving despite ice and snow.
Rock salt is composed of the mineral halite (sodium chloride) and occurs in thick beds deep beneath parts of Cheshire, Yorkshire and Northern Ireland.
'Rock salt is an important mineral which becomes critical to the British economy during winter weather. As part of our role in monitoring all UK minerals, the British Geological Survey provides a comprehensive range of information on UK salt resources, extraction, supply and consumption.'
The UK has large resources of rock salt in the ground that are sufficient to last for hundreds of years.
'The UK is, in theory, self-sufficient in salt. However, the bad weather can cause problems in terms of capacity to resupply local authorities — logistics of getting the salt from the mine to the highways depots once stockpiles built up over the summer are depleted — and so, in our globalised world, at times of maximum demand it is sometimes easier and quicker to import salt from elsewhere into a convenient port. Salt is not easy to stockpile in large amounts because it degrades over time when exposed to the atmosphere.'
In the UK, rock salt never occurs at the surface because the rainwater which soaks into the ground always dissolves it away. Almost all rock salt mined in the UK is used for road de-icing.
Table salt, and salt used as an ingredient in the manufacture of products such as household bleach and window glass, generally comes from brine which is pumped from the salt beds in Cheshire under carefully controlled conditions.
The salt formed 200–300 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).
Rock salt is mined at Winsford in Cheshire, Boulby in North Yorkshire and Carrickfergus in Northern Ireland.
For more information contact Andrew Bloodworth