I think they're just there for bits of cryptic story/atmosphere.
When I found the first one I totally thought it was an easter egg that was hidden.
I think they might be a connection to the Penumbra world or some "Frictional Games universe" since they serve the same purpose - hold the memories of people who touch them
I agree with HamStar's idea. That was my initial hypothesis. A link between the games.
I didn't see any orbs in Penumbra though. So perhaps the two types of artefact are not related, even though both of them are obviously very powerful.