what does a rock consist of
1 Allochemical rocks are those that contain grains brought in from elsewhere (i.e. similar to detrital grains in clastic rocks). 2  Orthochemical rocks are those in which the carbonate crystallized in place. 3  Allochemical rocks have grains that may consist of fossiliferous material, ooids, peloids, or intraclasts.any limestones (carbonate rocks in general) show characteristics similar to those of clastic sediments, like sandstones. Sandstones are composed of sand grains, a mud or clay matrix, and a crystalline cement produced during diagenesis.