Transparent Aluminum is a new, produced resource that is critical for many late-game units and Spaceship parts.

TransAlu cannot be found on maps. It must be produced. To do this, you will need to build a Transparent Aluminum Mill. This Future War Ear building converts 2 Aluminum into 1 Transparent Aluminum resource. It's the only way to obtain this vital late-game strategic resource. These mills require the Cold Fusion technology and a Freight Depot in the city.

Currently, you need the Commerce Policy tree enabled to build the Freight Depot, but in the next version of the mod, the requirement for Commerce will fall out. Until then, you'll need all of these things to build the mills that actually produce the resource.