18 Various Kinds of Opals
When most people think of an opal, they might think of a milky-colored stone containing a rainbow of stripes or flecks inside it. What many people don’t know is that they are incredibly diverse in appearance, and are not actually minerals. Opals are a solid, amorphous form of silica, and are classified as “mineraloids”. Like other mineraloids, such as amber, pearl, and obsidian, they lack structural order, or “crystallinity”.