Stone-cancer (as stone-leprosy) of Taj Mahal is due to formation of

Taj Mahal is made of marble (white stone), chemically it is CaCO₃. Acid rain corrodes marble. In presence of H₂SO₄, marble from the surface gets converted into CaSO₄ (gypsum) which has 2.1 times greater volume than marble, which causes increase in pressure on the surface of marble which leads to peeling, pitting and corrosion. This is called 'stone-leprosy' or stone-cancer.

$\begin{array}{l}{\mathrm{SO}}_2\mathrm{\hspace{0.17em}}+\mathrm{\hspace{0.17em}}{\mathrm{O}}_2\mathrm{\hspace{0.17em}}\stackrel{ }{\to }\mathrm{\hspace{0.17em}\hspace{0.17em}}{\mathrm{SO}}_3\\ {\mathrm{SO}}_3\mathrm{\hspace{0.17em}}+\mathrm{\hspace{0.17em}}{\mathrm{H}}_2\mathrm{O}\mathrm{\hspace{0.17em}}\stackrel{ }{\to }\mathrm{\hspace{0.17em}\hspace{0.17em}}\underset{\mathrm{Acid}\mathrm{\hspace{0.17em}\hspace{0.17em}}\mathrm{rain}}{{\mathrm{H}}_2{\mathrm{SO}}_4}\\ \underset{\begin{array}{l}\mathrm{Marble}\mathrm{\hspace{0.17em}\hspace{0.17em}}\mathrm{of}\\ \mathrm{Taj}\mathrm{\hspace{0.17em}\hspace{0.17em}}\mathrm{Mahal}\end{array}}{{\mathrm{CaCO}}_3}\mathrm{\hspace{0.17em}\hspace{0.17em}}+\mathrm{\hspace{0.17em}\hspace{0.17em}}{\mathrm{H}}_2{\mathrm{SO}}_4\mathrm{\hspace{0.17em}\hspace{0.17em}}\underset{ }{\to }\mathrm{\hspace{0.17em}\hspace{0.17em}}\underset{\mathrm{Stone}\mathrm{\hspace{0.17em}}-\mathrm{\hspace{0.17em}}\mathrm{cancer}}{{\mathrm{CaSO}}_4}\mathrm{\hspace{0.17em}}+\mathrm{\hspace{0.17em}\hspace{0.17em}}{\mathrm{H}}_2\mathrm{O}\mathrm{\hspace{0.17em}}+\mathrm{\hspace{0.17em}}{\mathrm{CO}}_2\end{array}$