What are they?
Crystal Candies are a shimmering frozen layer over your usual Candies. You'll need to crack this casing to access the sweet contents underneath.
Matching trapped Candies will break down the Crystal layer, but you'll need to remove the Crystal if you want to reach the Candies underneath.
Candies covered by the Crystal will count in a match, but you won't be able to tap them, but you can move an exposed Candy to a space underneath the Crystal.
To help illustrate this, the image below shows that you can move the orange Candy under the Crystal, but you cannot move the blue Candy out from underneath, as the Crystal will stop you.
You may sometimes find Crystal Candies placed on the board that don't have Candies trapped inside. If you match Candies lower down on the board, any Candies at the top of the board will glide underneath the Crystal into any empty spaces you make.
To make the Crystal crash, why not try using wrapped Candy blasts or trigger a Striped Candy?
Different Boosters and Special Candies will have a different impact on the Crystal be sure to try out all your options. Get cracking!