A person? - No.
A place? - No.
A substance? - No.
An item? - Yes.
Did it exist in the First Age? - This is up to conjecture, but most likely yes.
A weapon? - No.
Is it an Elven Craft? - No.
Was it made/manufactured? - Difficult. Not exactly made, I'd say, but it was most probably shaped or worked to some degree.
A dwarf treasure? - Not a treasure...
Alright then, does it belong to the dwarves? - Yes, I think you could say that.
Is it valuable? - It is dear to them, but not in the same way as gold and jewels.
Mirrormere? - No...
Is it located east of the Anduin? - No.
Is it cram? - No. (See above - that would be a substance rather than a single item.*)
*(except if you mean the legendary Cram Cake of Durin that has been preserved and revered by the Dwarves since the First Age till it's become hard as stone, with runes made of icing on it... like a petrified
lebkuchen heart
)