Final answer:
The rock in question is a fine-grained, dark-colored sedimentary rock, likely composed of angular fragments and characterized by a layered structure. The grain size and shape indicate a short transportation distance from the source and some degree of weathering.
Step-by-step explanation:
The description provided suggests that the rock in question is a sedimentary rock. Sedimentary rocks are typically characterized by the size, shape, and pattern of their grains, which are pieces of minerals or older rocks that have been transported and deposited by water, ice, wind, or gravity. The dark color and composition from smaller pieces of irregularly shaped rocks indicate that it could be composed of fine to coarse grains with angular fragments. Sedimentary rocks often have grains that are layered or bedded as a result of their mode of deposition.
The rock may exhibit a wide spectrum of grain sizes based on the descriptions given but is likely to be fine-grained, as sedimentary rocks of this type do not have grains large enough to be distinguished by the eye. Furthermore, the grains might be angular, suggesting a relatively short distance of transportation from their source, and their pattern may suggest that the rock has experienced weathering, but preserved bedding or layering structure that can indicate its depositional environment.