Arcanum

A magical tool used to store the knowledge of spells, that may also be capable of storing usages of spells as well.

Mechanics & Inner Workings

Like many elven magical tools, arcanums are crystals containing enchantments woven into them.

Item type

Magical

Rarity

The rarity of an arcanum depends on location and its power level. 
Low-level arcanums are extremely common in the Elven Realm, and are used in place of the grimoires found in the Human Realm - serving the same purpose of solely storing the knowledge of a spell. They have limited slots for this knowledge, and most are already full of basic spells and intended for children still learning. 
Mid-level arcanums are uncommon in the Elven Realm and rare elsewhere - able to store knowledge of spells and a low number of usages. They have a larger storage space as well, and all elves serious about the study of magic obtain an arcanum of this level. However, they are only able to store one usage of a spell per "slot" taken up by that spell, and using the spell consumes its entry in the arcanum. Do to the enchanctments involved in their construction, those on the lower end can only store each spell once - but those on the higher end are able to store multiple copies of the same spell. A caster will need to rerecord a spell after its usage, which is a time consuming process achieved through meditation. 
High-level arcanums are able to store multiple usages of spells, and the entry of the spell is not consumed with usage. This is due to the spell knowledge slots and spell usgae slots being differentiated in high-level arcanums. However, this uses up more storage space - meaning that high-level arcanums store less spells than mid-level arcanums. Only the most dedicated and powerful scholars of magic obtain these rare and difficult to make arcanums, usually reserveing them for their strongest and/or most complex spells. 
Divine arcanums are those constructed by a deity, and can have practically unlimited space for spell knowledge and usages. Dieties are known to grant them for various reasons - Udhai, the Frost Elven Goddess of Magic, is known to grant them to the disaffinitied, as their ability to learn a wide range of magics pleases her.

Raw materials & Components

Arcanums are built from the components of magical creatures, most often bone, and fashioned into some form of mantle or necklace. The central component is a large stone to hold the spells within, which starts at the size of an acorn at the lower end and can be as large as a an adult hand at the higher end. The setting needs to be constructed from a magical material to keep the ambiant magic of the arcanum from deteriorating it, but there are no set rules on what the material should be.
Some chose materials that reflect their affintinities - such a light magic user using a stone from a desert region and the bones of an animal from the same area, while a water magic user might use a stone found in a coastal region and magical fish scales. Others may chose based on personal aesthetics or simple availability.