I’ll add that not too terribly long ago I used a microplane grater to grate up a bunch of white soap that I plan to use as snow. The starting soap was about the consistency of parmesan. After some air drying, the little grated pieces were easy to crunch into smaller bits with my gloved hand. This is why I think it might be possible to turn finely grated soap into smaller, flattish bits that could pass as a mica line without looking like little chunks. When I blitzed fairly dry soap in a coffee grinder, I ended up with small chips of varying sizes and soap dust. I separated the chips out with a fine mesh strainer and used them to decorate the top of a new batch of soap. I didn’t try to use the dust for anything because it looked grey (original soap was multicolored), but it may have been a good size for a faux mica line.