What are the screens made of on iPod nanos?

Hi I am looking to buy an iPod nano, most interested in 6th gen but everything from 4th onward looks decent to me... My current music player is last years model of the 8gb Sony Walkman. The very first time I put it in my pocket and went for a walk, the coins in my pocket made quite the mess out of my screen. The sound quality on the unit is amazing though... If I am going to invest in a new player, it has to have a scratch resistant screen like gorilla glass. What are the screens made of on iPod nanos and how well do they perform against being in a pocket with things such as coins, keys and a lighter?

Thanks in advance for any helpful responses 😀