In Dark Cloud 2, Georama elements are items that will be mainly used to make things in the Georama mode. There are many of Georama elements and this page lists all of them.
In-game description for every Georama element : "Georama element."
Since the Carpenterion can build buildings, trees, piers, etc..., Georama materials are used. But since it can also make rivers, lamps, things that produce "life", that's why Georama elements are also required.
Georama elements are common items that are found pretty easily in Dungeons' chests once Georama is unlocked. Like most common items, you can carry 999 of each Georama element.
Apart from Georama, those elements are also used in Inventions, in order to make items. They can also be used to increase weapons' stats.