What is the cap on the SMART bottle made of?

The original EQUA Smart designs – Snow White, Pink Blush, and Dark Grey all have a real marble top:

• EQUA Smart Snow White – Carrara Bianco or white Carrara marble originating in North Tuscany, Italy.
• EQUA Smart Pink Blush – Palissandro Bluette Nuvolato Chiaro marble originating in Italy.
• EQUA Smart Dark Grey – Black limestone Drenov Grič originating in Slovenia, Europe.