The lava from Indonesia's Kawah Ijen volcano has an electric blue appearance. Large quantities of sulfuric gases emerge at high pressures, exposed to oxygen in the air and are ignited by the lava producing a blue flame. It is not the lava itself that is blue, but the sulfur combusting producing a neon-blue flame. https://en.wikipedia.org/wiki/Blue_lava https://www.smithsonianmag.com/science-nature/why-does-indonesian-volcano-burn-bright-blue-180949576/