Transparent Aluminum

Aluminum Oxynitride

Also called AION and normally sold by the name ALON.

It is glass-like very strong ceramic used as the crucial outer layer of experimental transparent armor being considered by the US Air Force, for the windows of armored vehicles. Other applications include semiconductors and retail fixtures.

Such a material might be a candidate for use in the view ports of a pressurized lunar vehicle. ALON might be the pressure retaining pane with a vacuum space of a perhaps six centimeters between it and a thin outer pane of soda glass to break up small meteoroids and absorb scratches. The outer pane would be frequently replaced as a maintenance item.