>Blackstone
Interesting name.
The Black Stone is a rock set into the eastern corner of the Kaaba, according to Muslim tradition, dates back to the time of Adam and Eve.
They say it was white as snow when it fell from heaven to show where to build the first temple, and turned black from sinners touching it.
Good old symbolism.
>at the centre of the earth, where Satan is held in bondage
For just as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth.
But do not forget this one thing, dear friends: With the Lord a day is like a thousand years, and a thousand years are like a day. - 2 Peter 3:8