Generally, if a piece of stone is about a hand and a half-hand or less,
it is considered as "stack".(Approximate dimensions are 4" in width;
length is irrelevant.) These pieces of stone are the smaller pieces.

On the other hand, if it is larger than a hand and a half-hand,
it is considered as "regular" or "cap" rock.

The thicknesses of rock can be classified as "thin", "medium", or "thick."

Field stone is a type of aged sandstone rock.  It also appears
somewhat greyish in color, as compared to flagstone. It is
obtained from the top of the ground and has an aged appearance.

Applications for field stone are also often contingent upon the thicknesses
needed for each application.  i.e., the thin "stack" can be used for stacking
of walls and for dwelling foundations.  The medium "stack" can be used for
rock house construction.  Thicker field stone can be used for
retaining walls.