Halite – Day 23 of the Mineral Advent Calendar

This holiday season, why not get a mineral every day instead of chocolate? Today’s mineral is Halite find out more about it below..

It’s December 23rd and if you have finished work and are lucky enough to have tomorrow off, you might now very be….

If so, please be safe when driving back; if the rest of the country is anything like Devon tonight the roads are pretty wet!! Fortunately (or not, depending on how much rain you get) that means we probably won’t see any of a mineral that is usually EXTREMELY common this time of year – no not Ice, but it’s related – that is rock salt, used in grit to keep the roads safe. The reason salt is used to grit roads is because it lowers the freezing point of water (meaning it has to get much colder before the water will freeze), though this only really works when the temperature is above -5 degrees. In this paper by Ari Venäläinen, researchers tried to use the mean air temperatures to gauge how much salt would be used in Finland during the winter period, but as I’m sure you can guess, the result was that although air temperatures give some guide as to how much salt people use on the roads, modelling accurate amounts was dependent on a combination of issues, including road maintenance and people’s behaviour.

Salt is most definitely a mineral, as anyone who has ever been to a salt mine can attest. Rock salt, more properly called Halite when in it’s mineral form, is something that although we may be more familiar with it on the kitchen table, is essential for safe driving at this time of year.

So stay safe on the roads if you are driving home tonight, and check out this amazing microscope image of a Halite crystal taken by Dr Natasha Stephen in Plymouth University Electron Microscopy Centre.

A lovely Halite crystal photograph taken by Dr Natasha Stephen at the Plymouth University EM centre.

A lovely Halite crystal photograph taken by Dr Natasha Stephen at the Plymouth University EM centre.

Chemical formula: NaCl
Colour: Colourless, white, yellow, red, purple or blue
System: Isometric
Hardness (Mohs):
Can you find it in the UK? Er yes! (In fact it is still mined in Cheshire)


Cheshire's salt mines are still very much active! Image from the BBC.

Cheshire’s salt mines are still very much active! Image from the BBC.

Halite is a common mineral all over the world and although I have been talking about it in it’s mineral sense (that can be mined – a type of mineral called an evaporite), let’s not forget that you can also get halite when it is exsolved out of (as opposed to dissolved into) sea water! This can cause Halite to crystallise in sheltered spots around the coast, so keep an eye out for these little white-pink cubes, you may find it more easily than you think!

For more information about Halite please visit the MinDat website.

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