Dry Ice & Silica ($$\text{SiO}_2$$)

Dry Ice: Solid $$\text{CO}_2$$ held together by weak van der Waals forces, undergoing sublimation at $$195\text{ K}$$ ($$1\text{ atm}$$) without passing through a liquid state.

Silica ($$\text{SiO}_2$$): Three-dimensional covalent network solid where each silicon atom is $$sp^3$$ hybridized and tetrahedrally bonded to four oxygen atoms via single bonds ($$\text{Si--O--Si}$$ linkage angle $$\approx 144^\circ$$).