Molten lava erupted by volcanoes freezes very quickly, leaving holes where gas bubbles used to be. These holes in the rock soak up fluids like a sponge. A variety of minerals can settle out from the fluids and collect along the bubble walls. You are looking at a cut through the edge of a bubble in volcanic glass. This bubble has been completely filled up. A thin layer of quartz crystals was deposited first, followed by the layer of celadonite (orange). A piece of celadonite later broke off the wall and is sealed in place by calcite which filled the rest of the bubble.

Crossed polarizers