Incredible geysers and limpid opalescent pools belching hot sulfurous fumes populate the Midway Geyser basin. The most spectacular feature is the 300 feet diameter Grand Prismatic Spring. The water is rich in pigmented bacterial mats and minerals that create the vivid colors, starting with blue in the middle, to greenish due to chlorophyll and reddish due to carotenoids outside, graded by the water temperature.
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| Unearthly colors near Grand Prismatic Spring (aerial view at bottom of page) | Turquoise Pool | Beauty Pool |
Silex spring at Fountain Paint Pot
