  Silica or SiO$_2$, the main constituent of earth's rocks has several 3D
complex crystalline and amorphous phases, but it does not have a graphite like
layered structure in 3D. Our theoretical analysis and numerical calculations
from the first-principles predict a single-layer honeycomb like allotrope,
h$\alpha$-silica, which can be viewed to be derived from the oxidation of
silicene and it has intriguing atomic structure with re-entrant bond angles in
hexagons. It is a wide band gap semiconductor, which attains remarkable
electromechanical properties showing geometrical changes under external
electric field. In particular, it is an auxetic metamaterial with negative
Poisson's ratio and has a high piezoelectric coefficient. While it can form
stable bilayer and multilayer structures, its nanoribbons can show metallic or
semiconducting behavior depending on their chirality. Coverage of dangling Si
orbitals by foreign adatoms can attribute new functionalities to
h$\alpha$-silica. In particular, Si$_2$O$_5$, where Si atoms are saturated by
oxygen atoms from top and bottom sides alternatingly can undergo a structural
transformation to make silicatene, another stable, single layer structure of
silica.
