Diamond..... Crystal Leggings? (need Help)

I'm kinda new to the server, I was wondering about a legging called crystal (lvl. 69), i got one like 2 weeks ago. It's an iron leggings, until someone showed up and I saw he had a a crystal diamond leggings (also lvl.69)

Is this a feature or a mob drop?

 

Im pretty sure the old ones have diamond texture. There's no difference anyway.
@Spectical

 

The diamond Crystal was a mob drop from the past. Before Gavel Update has been released, you could get Crystal Diamond Leggings, but now only Iron Crystal leggings, so diamond once are not obtainable anymore, but the price is the same as normal are, you are not allowed to sell it for a higher price just because it's diamond.

 

oh ok thanks

 

Players still keep things like diamond crystals, millenniums, blue masks, etc as collector's items