The Primordial crystal is a Cerberus drop that upgrades a pair of Dragon boots into Primordial boots. It is not worn or used on its own. It needs 60 Runecraft and 60 Magic to apply, and the upgrade is permanent.
Grand Exchange price history
What the Primordial crystal makes
The crystal has one use: you apply it to a pair of Dragon boots and they become Primordial boots. The upgrade needs 60 Runecraft and 60 Magic, boosts do not count, and it gives 200 XP in each skill.
The process cannot be reversed, so you will not get the crystal back.
The finished boots are what you are paying for. Primordial boots need 75 Strength and 75 Defence to wear and show +5 strength and +22 to each melee defence. Dragon boots show +4 strength and +16 / +17 / +18 defence, and need 60 Defence.
How to get the Primordial crystal
The crystal is a boss drop and it is tradeable.
You also need a pair of Dragon boots, which you can buy separately. Use the live prices to total up the crystal and the boots against buying finished Primordial boots.
Is the Primordial crystal worth it?
The upgrade makes sense if you melee at 75 Strength and 75 Defence and want the best strength bonus the boots slot gives short of the Avernic treads, which are built on top of Primordial boots. The step from Dragon boots is small on paper: +1 strength and +4 to +6 defence depending on the melee style.
If you are below those levels, stay in Dragon boots, or Rune boots if you are under 60 Defence. When the totals are close, compare gear on the gear progression page.