Can Calcium Carbonate and Silica can be dissolved and reformed as a cement by the action of natural acids?
The presence of absence of broken shells made of Calcium Carbonate can determine if a soft or hard sedimentary rock is formed.
Sand stone is simply sand unless there is a chemical reaction between the dissolved Calcium Carbonate in the sand and an acid such as
I have found fossilized spark plugs off the coast of Oregon, sunset bay. The Calcium Carbonate in the water reacting with the rusting spark plug formed a cement that "glued" the rocks, sand and metal together forming a fossil. ( A fossil being any preserved evidence of living organisms)
So yes Calcium Carbonate does react to form a natural cement, under the right conditions, and this can happen very rapidly.