We report the discovery of Q-silicon with an atomic density of 60% higher than crystalline silicon while keeping the bonding characteristics the same as normal silicon. Distinct amorphous phases are created

when one

two

or three tetrahedra are randomly packed

and a crystalline phase of Q-silicon is formed when subunit cells are arranged along 110 directions with alternate holes. Nanosecond laser melting of amorphous silicon in an undercooled state and quenching have created Q-silicon with robust ferromagnetism compared to the diamagnetism of silicon. The blocking temperature of Q-silicon is estimated to be over 400 K

thus opening a new frontier for spin-based computing and atomic-level storage.