Goshiki-iwa Outcrop
This 200-meter section of exposed rhyolitic tuff is known as Goshiki-iwa (literally, colored rock). The colors result from variations in the rock’s mineral content and the leaching and oxidation of iron, which occurs during weathering.
- The light gray rocks have a high silica content. Rhyolitic tuff often contains quartz and other glassy minerals, all rich in silica.
- The yellow, brown, dark red, and black rocks are thought to contain iron oxide minerals such as hematite or goethite.
- The green rocks suggest the presence of a mineral such as chlorite.
