Blue Coral.

Blue coral or Heliopora coerulea is a coral and the only species in the family Helioporidae and the only Octocoral known to produce a massive skeleton. This skeleton is formed of aragonite, similar to that of scleractinia. Individual polyps live in tubes within the skeleton and are connected by a thin layer of tissue over the outside of the skeleton. It is found extensively throughout the Indo-Pacific where it is a common member of shallow coral reefs.

Due to its unusual blue colour and being fairly tolerant of conditions it can be used in tropical aquariums.

A syrup extracted from the coral is commonly used in "Bubble Tea" drinks found in and around south east asia.