Rainforest (Ryolite) Jasper
Ryolite is a relatively rare volcanic rock that exists naturally in mottled colors of brown, mossy green and a deep rusty-red (terracotta). This intricately patterned stone begins in a molten state that cools 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 out in particles ranging from ash all the way up to big blocky chunks. The decorative rock that is cut into the ornamental stones used for jewelry, is formed when the lava flow "bands" and is literally frozen into the stone. The stones with more green are often called Rainforest Jasper because of the forest-like colorations--But they are actually igneous rock with a high silica content — chemically identical to granite. The patterns on each stone vary greatly. Rainbow or Peacock Rhyolite (more often Peacock Jasper) are lighter in color than typical Brown and Green Rhyolite, and have more distinct areas of red banding. An interesting tidbit: Although the terms Ryolite and Rhyolite are generally used interchangeably, geologists refer to "Rhyolite" (also called Mushroom Rhyolite) as being grey, brown, or having a reddish-terra cotta hue. Both varieties are found in the USA and Africa. This website has a separate listing for Mushroom Rhyolite.