Toa stones were powerful relics which loomed large in the history of the Matoran civilization. From all evidence, it appeared that Toa stones were ordinary rocks until they were invested with some portion of a Toa's power. Once this is done, they seemed always to be linked to the creation or the coming of Toa heroes. At least two sets of Toa stones were known to have existed: the ones created by Toa Lhikan which created the Toa Metru, and the ones created by the Toa Metru which were used to summon the Toa Mata to Mata Nui. It was unknown if other Toa stones existed.
Lhikan placed each stone in a thin sheet of metallic protodermis that looked like foil. He wrapped the stone in it and sent six streams of energy from his hand which merged into a single white lance of power and flowed over the wrapped stone. When he was done, the sheet was sealed around the stone, and the symbol of the three virtues was imprinted upon it.
Toa stones were well-known items. Almost any rock could serve as a Toa stone. A Toa would take it in hand place a minute portion of his energy inside. Later, it could be used to trigger the transformation of a Matoran into a Toa. A Toa stone was passive, merely a receptacle for Toa energy.
The Toa stones which Takua retrieved were rocks with a small portion of Toa power in them, designed to spark the transformation of Matoran into new Toa.
The Toa stones collected by Takua sent out a signal to draw the Toa Mata's canisters to the island. They were a failsafe in case the canisters malfunctioned.
A Toa stone didn't necessarily have to be used at a Toa Suva.
Toa stones themselves didn't turn Matoran into Toa, they merely unleashed the power that was already inside the Matoran.
Only a Matoran destined to be a Toa would have the power that could be triggered by a Toa stone.
It only took a fraction of a Toa's energy to make a Toa stone. A single Toa could perhaps make dozens or even hundreds of Toa stones before running out of Toa power.