Glorious glass – worth more than gold?

That was my thought too..

cooking fires on the beach i'd imagine.

Perhaps its from metallurgy? or maybe cooking fires that got out of hand in a home made stove?

Very large bonfires might reach about 2000F. Sand melts to glass at 3000F.

Obsidian is volcanic glass. We might have also seen glass near meteorite impacts, or perhaps lightning strikes. If not from those natural phenomena, we might have discovered it as a side product of smelting copper, or perhaps some shop's apprentice messing around with the furnace.

Dirt in certain places has the right mix of minerals to melt at much lower temperatures than sand alone, and would have made melted lumps under large campfires. The source material might have been natural, or the side-effect of some other industry, such as slag from smelting.

You can imagine the sequence of steps: Kids playing with sticks pulling out the red-hot gooey mess. Trying to make the gooey things solidify into interesting shapes. Realising the results are durable and shiny, if a bit ugly in colour. Then experimenting with mixing different kinds of dirt and clay to change the colours. Eventually discovering that translucent is possible, then transparent, etc...

https://en.wikipedia.org/wiki/History_of_glass

Induction cooktops are.

a lot of them are, like ceran cooktops