There are 20 different types of Octec crystal, and you must install one of each in the statue to complete the test. When you begin the test at a University of Architecture, you will be given two crystals. You may then receive crystals from School of Architecture five more times times, for a total of 12 crystals. You may only receive crystals once every eight hours. All the crystals you receive will be of the same type. You will need to trade with other players to complete your set of 20. A player-built institution, the Crystal Exchange, exists to optionally assist with swapping crystals of one type for another.
The 20 crystal types are:
A Statue of Octec's ghost is built at a small construction site, and requires the following:
It is possible to install a second set of 20 crystals (for a total of 40) in a statue. A double-rigged statue may be used to make a diamond-tipped shovel, once a month. Diamond-tipped shovels are 50% more effective than fine steel shovels.
(See also: Tests, Crystal Exchange)
Note: While the above (and the .info site) both list it as "steel cable", it will just be listed as "cable" in inventory.