Answer:
The letter S is added to pluralise most words in the English language. eg. Letter to Letters Word to Words and Language to Languages. But I am a word that is pluralised with the addition of the letter C.
What can you break even if you never touch it?
I can go through glass without breaking it.
I am not alive but I can die. What am I?
I am cracked by Indiana Jones.
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.