Deepslate

Deepslate is a stone variant found deep underground in the Overworld that functions similar to regular stone.

Breaking
Deepslate can be obtained only by mining it using a pickaxe with the Silk Touch enchantment, otherwise it drops cobbled deepslate. If broken with any other tool, it drops nothing. The breaking time for Deepslate is roughly twice the time for Stone.

Natural generation
$$, deepslate makes up the majority of the solid blocks generated below y = 0 in the Overworld. Stone is gradually replaced from y = 0 to y = -7 until completely replaced by deepslate. Deepslate also generates in mineral veins, attempting to generate twice per chunk in veins of 0-862, from levels 0 to 16. These veins can replace stone, granite, diorite, andesite, and tuff.‌

If iron, gold, diamond, redstone, or lapis lazuli ore generates in deepslate (or tuff), it will become its deepslate variant. Coal, copper, and emerald ore will not become their deepslate variants, despite having overlap in the levels they generate.

$$, deepslate can generate in the Overworld in the form of mineral veins, attempting to generate 10 times per chunk in veins of size 0-160, from elevations 0 to 16. All ores generated in deepslate blobs will transform into their deepslate varient.

Smelting
Deepslate can be smelted from cobbled deepslate.

Usage
Deepslate can be used as a building block.

Cobbled deepslate
Deepslate can be mined using a pickaxe without the Silk Touch enchantment to obtain cobbled deepslate.

Silverfish
Silverfish can enter and hide in deepslate, creating an infested block.

Trivia

 * According to Brandon Pearce, the reason for changing the name "Grimstone" to "Deepslate" was because the word "Grim" had too many connotations related to a negative feeling and therefore did not accurately describe the block as to what it actually was. The name "Deepslate" was eventually chosen because of its location within the world and to more accurately represent that it is a type of slate.
 * Similar to stone, the orientation of the texture varies depending on the coordinates.