The pattern is made of tumbling block hexagons, each made from three 60 degree diamonds (light, med, dark).
The effect shown in the picture is achieved by making each hexagon into a rhombus so they can then easily be pieced together in rows (or columns).
The rhombus is made by adding two 60degree equilateral triangles (NOT HST), one in each opposite corners of the hexagon.
The triangle side size is the same as the finished side of the diamond, plus seam allowances.