This stone has the same appearance as that which makes up the bulk of a monolith's structure, but you are not quite able to duplicate its indestructability.
Its crafting is classified as Eldritch Knowledge and must be researched before used, but the blocks can also be obtained by using an Arcane Bore to mine the tunnels and chambers inside of monolith structures.
This stone doesn't project a shadow. It has a light value of 3, and does not block light from other sources.
Testing shows that Eldritch Stone has an explosion resistance similar to Obsidian or Reinforced Stone/Glass. One layer of Eldritch Stone (in the form of a box) will stop the blast of an Industrial Craft Nuclear Bomb.