system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does the Arkenstone actually do?

Everyone wants it. What's it for?
gpt
If you read the Silmarillion, you find out just how old the Arkenstone actually is. Basically, it's a family heirloom over a couple of millennia. It also glows of its own accord, which suggests that it was formed in the ages before the sun and moon.