This item can be purchased from Merchants:
Aurulite drops in all Instanced Adventure Wing Dungeons introduced in the Catacombs expansion. It can drop from any mob in these dungeons. Aurulite is used to purchase Catacombs armor, weapons and jewelry from Catacombs merchants, similar to Darkness Falls seals.
There are 5 varieties of Aurulite, however they all hold the same value, the difference between them is the amount the drop in.
It's unlikely that you would get more than two types of seals in one dungeon. They do stack up to 1000.
Break Down of Aurulite: (values reflect 1.88 changes. Note: These changes are not retroactive and only apply to newly-dropped Aurulite.)
Chip = 5
Fragment = 10
Shard = 20
Cluster = 30
Cache = 40
Mobs that drop Aurulite will not be listed as the list would be exceedingly long, but rest assured you will find Aurulite dropping from all mobs in these dungeons.
This is also a possible winning for 1 card match in Trifecta.