Construction block

A dual construction block comprising a body substantially in the shape of a rectangular parallelepiped having a pair of end faces, a top face, a bottom face and a pair of side faces;

• vertically aligned transverse splitting grooves in said top and bottom faces midway between said end faces to define a pair of mirror image single blocks connected at their rear faces with said end faces defining front faces;
• a plurality of substantially identical parallel transverse grooves only in the bottom face of each single block, and extending thereacross from one side face to the other;
• said grooves being of constant cross-section and being spaced apart evenly between the front face and the rear face;
• and
• at least two ridges only on the top face of each single block, each said ridge being parallel with and in vertical alignment with one of said grooves, and receivable within a groove of a like single block, there being fewer ridges than grooves, and the outermost of said ridges being set back from the front and rear faces at least a distance equal to that between the front and rear faces and a respective second closest groove.