This crystal-like shape is known as an Opal Pineapple. In fact they are neither crystals nor pineapples. Opal is an amorphous mineral, meaning they have no crystal form. Opal pineapples are Pseudomorphs, which occur when one mineral replaces another making a cast of the original mineral. Opal has replaced the original mineral Ikaite, which only crystallises in near freezing conditions. This suggests that these pineapples had their beginnings in an ice age.