Adding to their rarity and singularity, the rarest of these precious stones grow in pure marble and are a beautiful, intense red. Here, we gathered the most gorgeous ruby engagement rings—that ...

The cushion-shaped, untreated ruby is mounted on a ring flanked by two pear-shaped diamonds ... a rare gemstone that changes color from red under incandescent light to green in daylight.

A spokesperson for Diamonds Factory Ireland said: "Worn by the Princess of Wales occasionally to match red outfits and accessories, this beautiful ruby ring was first seen on a visit to Poland.