Ice is a translucent solid block found only in snow biomes. Because of ice's slippery nature, a player will move more quickly on ice than on any other block at the cost of their mobility.
Due to its transparency, torches cannot be directly placed on this block. Ice will also melt and leave a water source block if the light level on any side (from light sources other than sunlight) is greater than 11. Conversely, a water block in a snow biome will eventually freeze into ice if exposed to the sky from directly above, and the light level immediately adjacent to the water block on all sides is sufficiently low (less than 13). This can happen at any time of day, and in any weather condition. If the highest adjacent light level is 12, an ice block will alternately melt and re-freeze when it receives a block tick, Ice can also be used to make water flow faster by placing Ice below a moving water source.
When 'super' sprinting with Quantum leggings, ice will cause you to move extremely fast - approx. twice as fast as normal 'super' sprint. If you turn off ice melting, you could feasibly create Ice highways for quantum legging users - it's the fastest way of travelling short of teleportation.