Rhyolite

Though at first glance it might look like jasper, rhyolite is an igneous rock with high silica content - chemically identical to granite. It cooled from a molten state (as hot as 2192°F), too quickly for crystals to form. Because rhyolitic magma and lava are so thick, they tend to build up pressure until a gas explosion in the volcano throws them all over the place in particles ranging from ash all the way up to big blocky chunks. The stone's mossy greens, browns and grays are reminiscent of a rainforest, and it presents interesting banding.