It would be interesting to show photos of what you use for bonsai, or horticulture.
From the colour, I’d say it’s what we call “pouzzolane”, (pozzolan in English: https://en.wikipedia.org/wiki/Pozzolan). “Scoria”, at least in French, is a very vague term referring to whatever hard particles are left from firing.
Here, we also use “Pumice”, another “by-product” of volcanism.
There’s plenty of pozzolan in the “Massif Central” in France, it’s easily found in garden centers: I just saw pallets of 15 litre-bags, 6-15 mm, priced 7.50 €. But I can get 30-litre bags of sifted 3-6 mm, or 1.5-3 mm, for the same price! And those who have a truck can get some for a ridiculously cheap price (a few euros a ton) if thy can drive about 300 miles 😉
Pozzolan, pumice, composted pine bark (3.50 € for 30 litres from the same supplier), and akadama, that’s what everyone in my club uses.
Pozzolan: doesn’t retain moisture that much, but the sharp edges helps the roots to ramify.
Pumice: retains a bit more water, but it’s appreciated for big containers. When dry, doesn’t weigh that much, so it’s easier to move the pots.
Composted pine bark: a must here because the water from the tap is very hard. Excellent also for mycorrhyzae.
Akadama: well, that for the best trees, considering the price ;-). I use it with any cocktail of the previous soils mentioned. I’m not a professional, just an enthusiast.
AlainK