Volcano Boss Chests are items that can be obtained by defeating the Magmoraug boss that can appear in the Volcano. It, like other Main Hub boss chests, can drop gems, crate keys, hoverboards and a pet. Volcano Boss Chests cannot be burned at the Incinerator in the Junkyard.
As of v1.103.0, this item can be converted by the Main Hub Gumball Machine into Gum. The exchange rate is 1:1.