The part of the Earth that contains seldom seen at the surface and are largely similar is the mantle.

Here's why:

* Seldom seen at the surface: The mantle is a thick layer of rock that lies beneath the Earth's crust. We can't directly see it because it's buried deep underground.

* Largely similar: While the mantle has different layers with varying compositions and properties, it's generally composed of silicate minerals and is largely similar throughout.

Let me know if you'd like to learn more about the Earth's mantle!