Vicker's and Knoop microhardness studies were carried out on grown calcium hydrogen phosphate dihydrate (CaHPO 4 ·2H 2 O) crystals over a load range of 10–50 g. The Vickers ( H V ) and Knoop ( H K ) microhardness numbers for the above loads were found to be in the range of 94–170 kg/mm 2 and 28–35 kg/mm 2 respectively. It was also found that these numbers increased with increase in load. The Mayer's index ( n ) was found to be greater than 1.6 showing soft-material characteristics. The fracture toughness values ( K c ), determined from measurements of crack length, were estimated to be 6 ± 0.5 × 10 3 kg m −3/2 and 4.5 ± 0.5 × 10 3 kg m −3/2 at 25 g and 50 g respectively. The brittleness indices ( B i ) were found as 2.3 ± 0.1 × 10 4 m −1/2 for 25 g and 3.7 ± 0.1 × 10 4 m −1/2 for 50 g. Using Wooster's empirical relation, the elastic stiffness coefficient ( c 11 ) has been calculated from Vicker's hardness values as 4.8 ± 0.5 × 10 15 Pa for 10 g, 9.7 ± 0.5 × 10 15 Pa for 25 g and 13.3 ± 0.5 × 10 15 Pa for 50 g. The Young's modulus was calculated as 1.5 ± 0.1 × 10 10 N m −2 from Knoop microhardness values.