Rock structural modules fashioned from natural rock strata are heavy. As such they are unsuitable for transportation. They are normally considered natural resources used in cave construction on account of their relatively low tensile strength. Typically, they are most produced by resource complexes from planetary rock rather than through factory production.
NB. Certain natural plants are exploited for timber that can be fashioned into structural modules. As modern materials are much lighter than natural ones, timber modules are generally classified as rock structural modules rather than structural modules. This is simply due to the mass of timber that is required to produce a module.