Try white cement, sifted peatmoss, vermiculite and sand.

You can't mix certain kinds of glass with cement. I forget which ones but it is online.
You don't need glass for a sparkle. Just use equal parts either white or grey cement, perlite, vermiculite and white sand. Billie

I've used combinations of small flaked mica (available from larger craft suppliers or online); silver and frosted glitter - not the patterned, punched variety. After brushing the partially cured tufa you get a natural sparkle similar to embedded mica and quartz.

Thanks, everyone

I see I have some experimenting to do :-)

I'll give a try with straight up peat/perlite/vermiculite and cement and I'll also give it a shot with the flaked mica.

I'll post pics as soon as I'm done :-)

Vermiculite only comes in small, rather expensive bags at my local shops. I was able to get a large bag of perlite at a much better price, but I made the mistake of not trying a smaller quantity first. The vermiculite was a brown-ish, mica like product and like liked it much better than the refrigerator white of perlite. Wish I had done more experimenting to begin with.

David

I just bought a container(margarine size)of "pixie dust" at Michaels crafts for $10. Looks great.

You can almost certainly get large...and I mean large, bags of vermiculite and perlite at a local garden supply store. It's inexpensive and lasts through many projects.