The colors present of the Grand Prismatic Geyser basin at Yellowstone National Park are due to an interesting combination of minerals and lifeforms. The milky blue features are due to silica in suspension in the hot water. A great deal of the red-orange that can be seen is due to iron oxides and arsenic compounds. The springs at the thermal basin that are emerald green in color are due to the blue of refracted light in combination with the yellow of sulfur lining the pool.