Obelisk

Obelisks are a mission item in Astroneer, used in a mission added in the Rails Update.

Source
Obelisks are found underground on Calidor in the mantle layer.

Uses
Obelisks are needed to be found and destroyed with Dynamite to obtain Shards for the They Belong In a Museum mission, ten Shards are currently needed to complete the Mission. Each Obelisk drops around 2-3 Shards when exploded, meaning on average you will only need about four Obelisks to obtain at least ten Shards. By grouping the Obelisks together, you can destroy many of them at the same time with one Dynamite.