Taken from the official Harry Potter Wiki site:
The graphorn is large and hump-backed, with greyish-purple skin tougher than that of dragons. It can repel most spells, has two golden horns, and walks on large four-thumbed feet.
Its horn is a highly prized potion ingredient, used in potions like Antidote to Uncommon Poisons. Graphorns are sometimes used as mounts by Mountain Trolls, but the Graphorn does not like it - it is more common to see mountain trolls covered in scars from a Graphorn.
In the Study of Ancient Runes, the Graphorn's two sharp horns are used to represent the number two.
You're looking for a small lock-and-lock container in Village Park. The trails back here are many and often windy, but if you follow the one near the dam is should get you to the cache. There are many briars around the cache so be careful! Please rehide the cache well and again, make sure everything is put back correctly. Thanks, and hope you enjoy.
In addition, a BIG thank you to RIclimber for providing the beautiful stamps for this series!