The powers that be in your local area are probably using the 'environmentally friendly agricultural by-product' grit.
Its called "Safecote", and is a mixture of salt, sugar and grit, which is reputed to last longer than traditional rock salt when spread on icy roads (it isnt flicked off the road towards the pavement by traffic). Its also meant to be less corrosive to cars too.
However, it can lead to some roads being slippy as hell, some people think its the sugar that causes it, others claim the mixture of sugar, salt and grit grind together when vehicles pass over it and polish the road surface.