Hydrazine

is one of the resources in Astroneer. It can be mined from veins on the surface, in the first levels of caverns, or from using a Fuel Condenser module.

Hydrazine is used as fuel for the Shuttle, Spaceship and Thruster

It's very useful for trading on the Trade Platform because you can get it so easily with the Fuel Condenser, though it has been reduced in sale value to 1, and the Fuel Condenser has been nerfed, making it tedious to trade for rarer materials.

It looks like a Tank but with purple liquid inside and the Attachment Point is on the side.