Marquise Diamonds: Shape, Proportions, Certification, and Buying Checks Marquise diamonds are elongated brilliant-cut diamonds recognized by two pointed ends and a curved, boat-like outline. Their long shape can create a large face-up appearance for their carat weight, but the outline, symmetry, length-to-width ratio, bow-tie effect, girdle, and grading report matter more than carat weight alone. This guide explains how to assess a marquise diamond before comparing stones or choosing a seller. What makes marquise diamonds different from other shapes? For