Firstly, it's unrefined so it has no nasties that come with the processing of rock salt and because it's unrefined it has over 50 trace elements such as magnesium, potassium and calcium. These help keep the balance of your electrolytes Perfect.
Secondly, your skin and sea water have an neutral balance. The salts, as well as exfoliating, absorb wastes and can be washed away when you rinse. Not only that, but sea salt is lower in sodium than rock salt - that's good if you eat it but just as good when it come into contact with your skin.
Thirdly, the very nature of the salt is 'flakes' not small hard crystals. Flakes are kinder and easier to rub against your skin
We don't use rock salt, yes there's some groovy types of rock salt out there that sound great and look great too - Himalayanrock salt for instance. BUT, they're all still rock salt.
When it comes to your skin only use the best, Sea Salt.