Why are marble chips not soluble in water?

Because Marble chips, Calcium carbonate, (CaCO3), require an acidic pH (less than 7) in order to dissolve at a useful rate*. The lower the pH, the faster it reacts. At a pH of ~8 or higher, it loses almost all of its aqueous solubility.

* Actually marble chips are slightly soluble in water. This is why they make such great stalactites and stalagmites. However, for most practical purposes, they are insoluble in water because they dissolve at a very slow rate, slow enough to be impractical for almost any useful purpose.

Related Information:

Decomposition occurs at various stages and many products and byproducts are formed, depending upon the pressure, temperature, and pH, all of which tend to vary at given stages of reaction. It decomposes, more than dissolves. Products can include:

CaO,

Ca(HCO3)2,

H2CO3,

Ca(OH)2,

Ca+2,

CO3-2,

HCO3-,

H+,

CO3-2

CO2

H2O,

OH-,