Only carbon from the Group 14 elements forms stable double bonds with oxygen under normal conditions. When frozen, carbon dioxide is known as "dry-ice". A non-molecular single-bonded crystalline form of carbon dioxide (phase V) exists at high pressure.

Amorphous forms of silica (a-SiO₂) and germania (a-GeO₂) are known at ambient conditions but only recently has an amorphous, silica-like form of carbon dioxide, a-CO₂. This is labelled a-carbonia and made by compression of CO₂ at room temperature at pressures between 40 and 48 GPa (that's a staggering 400-500 thousand atmospheres).