Knowledge crystals were objects used in Knowledge Towers to store information. Data could be recorded in the crystal by means of physical contact with a scholar, but the operation needed to be triggered by the will of that scholar.
A knowledge crystal was a little larger than Toa Nuju's hand. If tossed onto the ground of Ko-Metru, a new Knowledge Tower would start to grow rapidly from where it landed. The new tower would grow to full height in mere seconds.
Knowledge crystals about the size of Matoran's hand were used to grow new Knowledge Towers. They were thrown into special cradles located at different places in Ko-Metru, from which they grew at a rapid pace until a new tower stood alongside the old ones.