This is Litracon. Concrete blocks that use 4% optical fibers throughout as an aggregate. The cool thing is that makes the concrete translucent.

Technical data
Form:
prefabricated blocks
Ingredients:
96% concrete
4% optical fibre
Density:
2100-2400 kg/m³
Compressive strength:
50 N/mm²
Bending tensile strength:
7 N/mm²
Finish:
polished

So much nicer that those horrendous glass bricks from bad 70's architecture.

The Company