Castle Geyser features and Scanning Electron Microscope image of algal filament in a silica sheath

On the left is Castle Geyser during an eruption with a pool from nearby Tortoise Shell Spring showing photosynthetic pigments at the bottom. The middle image is of a small pool in the Geyser Hill Group in the Upper Geyser Basin with an outflow channel full of yellow, green, orange, red, and brown pigmented phototrophic microbial mats. On the right is an SEM image of a single algal filament (desiccated due to drying) inside a silica sheath—silica has precipitated around the outside of the filament, with small spheres of silica attached to the sheath.