Main crystalline component of calculus is
Hydroxyapatite
Octacalcium phosphate
Magnisium whitlockite
Brushite
Hydroxyapatite and octacalcium phosphate(constitute the bulk of the specimen) are detected most frequently in all supragingival calculus.
While in Subgingival calculus ratio of calcium to phosphate is higher subgingivally and sodium content also increases with the depth of periodontal pocket.