Which of the following crystal form is least found in calculus:: (A) Hydroxyapatite., (B) Magnesium whitlockite., (C) Octacalcium phosphate., (D) Brushite.
Answer is D. Hydroxyapatite 58%
Magnesium whitlockite 21%
Octacalcium phosphate  21%
Brushite 9%