Every item, object or creature is bound by varying mystical elements know as Aspects. Aspecst describe the object makeup and bent towards the magical elements. A simple stone may posess the aspect of Saxum (or stone) while more complex items like trees or even creatures can be made up of various different Aspects in varying amounts. There are close to 50 know aspects with more being discovered all the time.
To view what aspects an item posseses, simply hover your cursor over the item and press sneak (shift), and you will see what aspects that item has and what amounts of each.
Aspects that have somehow been separated from there object and purified is know as Essentia and is very valuable: both as a crafting tool and as a supject for magical research.