Shale cannot be directly turned into slate. They are both sedimentary rocks, but they represent different stages of the rock cycle.

Here's why:

* Shale is a relatively soft, fine-grained sedimentary rock formed from the accumulation of mud, silt, and clay. It's often layered and can be easily broken.

* Slate is a harder, metamorphic rock that forms when shale is subjected to intense heat and pressure. This process, called metamorphism, causes the minerals within the shale to recrystallize and align in a parallel direction, giving slate its distinctive, smooth, and often shiny surface.

So, to transform shale into slate, the following conditions must occur:

1. Burial: The shale needs to be buried deep underground.

2. Heat and Pressure: The increasing depth and surrounding rock layers provide intense heat and pressure.

3. Metamorphism: This heat and pressure cause the shale's structure to change, forming slate.

Therefore, it's not about turning shale into slate, but about allowing the natural processes of the rock cycle to transform one into the other.