Thank you for taking the time to look. I hope you enjoy the image!
[This is based on another marbled version of Glass Brick I (similar to Glass Brick II).
In Affinity Photo I used the perspective tool to make a vertical wedge.
Copied the layer flipped vertically and then blended both layers with each other (using Pin Light I think) against a deep blue background fill layer.
Finally used a 2-mirror distort filter to create the symmetry.
Did you want to know all that? Probably not! ... But it's pretty isn't it? (It looks nicer slightly zoomed so feel free to try pressing Z :)]