In Sylas' lore it reveals that petricite absorbs magic, which explains so much about why there are so many mages in Demacia, despite strong anti-magic sentiment, and why the land is so fertile when other areas with minimal magic presence like Noxus Prime and Shurima are usually arid or not fertile at all. A lot of petricite means a lot of magic is being absorbed from somewhere, right?
And then there's the fact that Ryze keeps all the World Runes in a vault under the petricite groves, the vault itself is even made of petricite. The lore says Ryze thinks the petricite suppresses the World Runes but we know that's not true anymore: It absorbs their magic.
No wonder there's so much magic in Demacia and evidence of magic, there's an archmage keeping like 20 runes of world-shattering power underneath an entire field of magic-absorbing rocks.