Crystalite

In order to get crystalite, you need to mine crystalite orre with a silk touch pickaxe (Diamond or netherite) it is found at Y lvl 13(AND ONLY Y LVL 13). You then smelt the ore in a furnace. Once done, you need 4 crystalite pieces (total) and 2 glass, 2 iron, and an enchantment book of protection.Use these items to craft a crystalite gem. You can upgrade your armor using a smithing table. 

You can also find crystalite pieces in end city masts, (94% 0 pieces,4% 1-2, pieces 1.5% 3 pieces, 0.5% 2 gems),bastion chests (96% 0 pieces, 3% 1-3 pieces, 0.9% 1 durability diamond helmet (crystalite upgraded, 0.1% 1 crystalite gem) or dungeons (98% 0 pieces, 1% 1 ore, 0.85% 1 piece, 0.13% 2 pieces, 0.02% 4 pieces

 It works like a totem of undying, but for armor. When your armor dies and its upgraded by crystalite gems, it will save the armor and it regain 80% of its durability.

Crystalite gems are also used for upgrading your helmet. Surround your helmet with 8 crystalite gems, and you get a permanent +2 blast protection In total, you can stack blast protection enchants with your permanent blast protect. 

Upgrading elytras will give it blast protection (permanent) also, but it needs to be done with an anvil, required level 50+

Last thing: If you wear upgraded armor with crystalite, any mob damage (arrow, explosion, potions, etc) will sometimes deal little to no damaged due to your clear crystalite. (13% probability this will happen)  details below:

2% helmet

5% chestplate

4% leggings

2% boots