Sandstar is the mysterious material that created Friends and Cerulean. Erupting from the volcano on Japari Island, it was originally experienced by the animals like a meteorite-like shower. To date, there have been three major eruptions of Sandstar and at least three types of Sandstar documented, pure Sandstar, crystallized Sandstar and Sandstar Low.
Sandstar in its most common form appears as shimmering light, often reflecting various colours. A Friend who uses a Friend Skill will have Sandstar spark from their body during said actions. If a Friend is hurt, they will also scatter sandstar from where they're injured. If the pure Sandstar make contact with the organic body of an animal or the remnants of an animal, a Friend will be formed.
After a Friend has been formed, their body shimmers with Sandstar for a short while as well, making them appear almost glowing. If Sandstar makes contact with a non-organic substance and fuses, a Cerulean is formed. When a Cerulean has its stone shattered, it breaks apart into several pieces that disappear into Sandstar rising through the air.
At the top of the volcano on the eastern side of Japari Island a large cluster of crystallized Sandstar rises up to the sky. Pure sandstar will often leak from it, trickling down during smaller eruptions.
It's unknown at the time what use the crystallized Sandstar have beyond being a reserve for pure Sandstar.
Sandstar Low is a new and dangerous type of Sandstar that is absorbed by Black Cerulean to increase their size and strength, causing what's known as a Colossal Cerulean. It's a danger to the park as a whole, and as such the volcano on Japari Island was set up with a filter to keep it from spreading.