Is sodium sulphate invariably effective in destroying any type of rock?
Sodium sulphate has been implicated as one of the most destructive weathering agents in many field observations and numerous laboratory studies. We hypothesize however, that sodium sulphate would not be invariably effective on any type of rock. To verify the supposition, a laboratory cyclic impregnation–drying experiment was undertaken. In addition to sodium sulphate, two other destructive hydratable salts, magnesium sulphate and sodium carbonate, were used to attack eight types of rock. In all three salt attacks, rock breakdown occurred only during immersion due to the exertion of higher crystallization pressure driven by the greater supersaturation reached after dissolution of the crystals precipitated during drying. Sodium sulphate was the most destructive salt in six out of the eight rocks tested, and even granite was substantially disintegrated. However, although probability is small, sodium sulphate indeed manifested its impotency against a relatively weak rock (Tago Sandstone). Contrary to its modest damaging power on other rocks, magnesium sulphate destroyed Tago Sandstone which could resist sodium sulphate attack. Sodium carbonate was the least destructive of the three hydratable salts. The general damage mechanism of hydratable salts, the process of damage of Tago Sandstone by magnesium sulphate and the possible reasons behind the impotency of sodium sulphate against Tago Sandstone are all investigated.