Aggregate
The sand and stone that make up roughly three quarters of concrete by volume. Aggregate provides bulk, dimensional stability, and most of the material's resistance to shrinkage.
What does aggregate mean?
Aggregate is often dismissed as filler, but its size, shape, cleanliness, and grading control water demand, pumpability, finishing behavior, and cost. Because aggregate shrinks far less than paste, mixes with more aggregate and less paste crack less. Local geology largely determines what a region's concrete looks and behaves like.
In practice
The stone in your slab almost certainly came from a pit within about fifty miles, which is why concrete behaves differently from one metro area to the next.