Source: Planar Adventures, pg(s). 244
Sapphire oozes are unusual intelligent oozes native to the wildernesses of Elysium. Heroic and altruistic by nature, these oozes often actively search for other beings to aid and rescue—something that, due to the oozes' own relative weakness, often means that they end up having to be rescued themselves. They occasionally find their way to the Material Plane, after which they usually attempt to join aspiring adventurers with whom to share adventures and do good deeds.
A sapphire ooze's most remarkable power is its ability to shape itself into a suit of crystalline armor sized to a creature roughly the size of the ooze itself, which can then be worn as regular armor. This armor is comparable in strength to mithral.