This unit is a center square set on point, rotated 45 degrees so it reads as a diamond, framed by four corner triangles that square the whole thing back off. It's often used interchangeably with the name Square in a Square, since a square rotated on point and a diamond are the same shape geometrically, just described from two different angles. Like several other units we've covered, it's a foundational building block rather than a standalone design, and its diagonal seams are notoriously easy to throw off if your seam allowance isn't precise, since there's no room for error once the center square is trimmed to size. It commonly shows up as a component inside larger, more elaborate blocks.