Diamonds are very special tokens, they can be used to buy other items:
its not on howrse anymore, sorry
you have to have 10 diamonds and they equal one pass
Before you use the diamond apple, but letting you know howrse got rid of the diamond apple so now there is only a golden apple.
You can use it to recredit your equestrian center's or breeder's reserve or 10 diamonds = 1 pass
You may get it in contests, getting some divines, or in the item exchange. [by the way... I'm applehorse1 on howrse!]
300 equus and if they complete the mission a diamond
You use it like any other meadow on Howrse.
Howrse no longer has illnesses.
It was only one pass like the golden apple.
The diamond cards are part of the howrse 2011 christmas cards. They are extremely rare and hard to find. The collector cards allowed puzzles to be completed (allowing a new divine: Greyfell) and a player to obtain BM/shop items.
You can use it when you wish to make your howrse immortal.
In the store, you can buy bonuses with diamonds. In the Black Market or Secret Market, you can use 10 diamonds as 1 pass. You can also credit equus. 1 diamond=2000 equus