The photo below shows an example of a rubble stone masonry wall. This wall is actually made from recycled broken pieces of concrete. You can see the gray areas of cement and the darker small stones inside of the cement. The darker granite stones work as an aggregate in the concrete mixture.
The picture below shows an up-close view of the of the broken concrete edges. You can see the small pieces of dark granite stone against the lighter cement in the concrete.
Another example of a rubble stone masonry construction follows below.