Brimstone

Brimstone is a layer block which is found below 1,125 to 3,110 or now 1,000 to 3,110 (approximate depth for the death barrier) and it's the block for the Abyss layer.

Info about the Abyss
The Abyss is a layer where ores rarely found in the Basalt layer are common. This layer stops spawning Sapphire, Ruby and Emerald, making Diamond the ore with the lowest cash. Abyss-unique blocks there are Lava, a crate explosive (Explosif), and Polonium. Quartz is common there.

To upgrade Brimstone mining speed, you need at least 10,000 coins if you haven't upgraded yet.