Remember the 2020 Deep Dark Trailer?
The new update was going to be long but exciting. There would be an extended height limit, new biomes, new WorldGen and so much more.
However, this didn't happen.
When Deepslate was added, it was called Grimstone which they thought gave a negative feeling for it's name, following the fact that it got renamed to "Deepslate."
The texture was ripped from a 3D render of Deepslate from the wiki. Mojang has the rights for that texture.
All of the other textures for Deepslate variants other than Deepslate are modified vanilla textures.
Some Screenshots are Here:

A Dark Cave

An Ancient City

All of the new blocks

