Tartar is mineralised plaque of yellow-beige colour and in supragingival position. Concrements on the other hand are hard mineralised plaques in subgingival position and of dark brown to blackish colour. The minerals stem from the saliva and inflammatory pocket secretion. The incorporation of blood components is responsible for the concrements' darker colour. Tartar is appositionally deposited, i.e., it develops on a layer for layer basis.
Tartar is only formed where plaque is not removed.