[Daily Photo] Black Opal Pool in Biscuit Basin, Yellowstone

This is the "Black Opal Pool" in "Biscuit Basin" of Yellowstone. The name "Biscuit Basin" comes from the mineral deposits around the fringe of Sapphire Pool. It is a hot spring. (You can judge by the steam above the pool surface.) However, it does not erupt like a geyser (間歇泉).  The two blue pools are where the hot water comes from.