This diveflyfish video of his EU geology experiment plasma melting pumice shows the low power (wattage) needed to melt pumice into a natural glass like substance using an electric/plasma discharge arc.
Malta quartz from limestone
Similar to the quartz found in the entrance stone to Malta's Mnajdra Temple.
Malta is an island made up of limestone, with supposedly no other type of native natural rocks.
Those rocks and stones that are found and are not limestone have said to be washed onto the island or into its greensand when being formed.
Yet a lot of quartz mineral is found in and on the limestone in various forms, from massive to micro crystals, from white to black colours.
Some of the Maltese quartz looks melted, like it has been formed on the limestone and then flowed downwards.
Some of it is found in grooves and others just inside the limestone.
Radioactive plasma glass
Plasma (Gentle) vs (Violent) - ionization from plasma (x rays etc) depends on type of plasma - at end of video he shows pumice glass has become slightly radioactive