Aquamarine Block is one of the many Decoration Blocks added by the Soul Forest Dimension. It can also be called a Storage Block.
Aswell as most of the Decoration Blocks this block is crafted with 9x Aquamarine Gems. After an Aquamarine Block is made, its content (the gems) can be easily re-obtained by simply placing the block in a crafting table.
a much more usefull function is the fact that you can easily store a lot of Amazonite Gems by turning them into blocks.