About
Diamond Rail is a custom item made especially for Blackblock.
Diamond rails allow minecarts to glide across straight tracks at breakneck speeds. Hold on tight!
Explanation
Spacing out your powered rails with diamond rails between them allows you to make minecart tracks that travel at breakneck speeds, twice that which can be achieved with an elytra.
The minecart will need powered rails to get it up to speed, but once it's going, it'll keep going unless there's a break in the track! Approximately 18 powered rails are needed to get the minecart going as fast as possible, then you can use about 2.5 stacks of diamond rails before needing to put down powered rails again.