I'm Stumped By What This Is!

This very unusual specimen was given to me by my sister who brought it back from South Africa. She didn’t know what it was but the person who gave it to her said I might like it as a rock collector. She forgot what the person said it was. On first inspection I thought it was Halite or something similar but it is much too hard about the same as quartz. It seems to be cubic in form and laminated.
Any ideas?
Many thanks

If hardness 7 then most likely chalcedony

Hi. I do take your point but the cubic nature of this piece made me wonder if this could be some sort of pseudomorph?