Size 20. Steel hook US 8
Advanced.

First 3 rounds = 1 5/8” or 4.2 cm diameter
Shape is like a pointy square with a scallop on each side. Shown on a pillow.

Pattern 3, pg 6, of Decorative Crochet.
Pattern Conchas de Santiago in Puntorama Ganchillo; shown on cover.
Called Bleu Metallique in 1000 Mailles.