My textbook says that the magnitude of strain produced is the same whether the stress is tensile or compressive. So the Young's modulus, which is the ratio of (tensile or compressive) stress to the longitudinal strain, should be the same for both compressive and tensile stress.

However, my textbook gives the Young's Modulus Of Bone for Tensile stress as 16 x 10^9 N/m^2 and for Compressive Stress as 9 x 10^9 N/m^2.

Since the Young's Moduli for other substances have been given only one value for both tensile and compressive stress, I was wondering if Bone is a special case, and if so, why?