[xeonmc]

TRANSPARENT ALUMINUM!?

Without a periodic crystal structure, it is likely to transmit light (see glass's transparency due to its amorphousness)

[BlueTemplar]

Aluminum Oxide (aka Sapphire, Ruby) and ALON are already transparent despite being crystals.

Being extremely hard and resistant they are used in applications like watch crystals, windows in grocery-store barcode scanners and armored car windows.