In my childhood, there was a spongy (ie full of bubbles) glass of a pale-green shade which was placed covering the stone-bounded graves in more than one of the church grounds near me, is there a name for this? It's a semi-transparent (the bubbles make it so) chip of glassy substance, but the sharp edges are not so sharp as to cut skin, they seem to have undergone some sort of foaming process to make them less dense than glass and have visible surface pits that appear to be part-spherical - as of bubbles of gas that existed before the glass set.
The graves had their usual scattering of pale-green ".......", the older ones with the darker green of weeds popping through....
The comments have lead to a perfect suggestion of an image by @KannE.
-Attribution indeterminate: Possibly Leo Reynolds 2019
A generic term, be-it colloquial or slang rather than a brand name is preferred.
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The chips were loose as-such, not cemented together, as I now gather terrazzo is.