Iceland is littered with fumarols, mud pools, hot springs and other geothermal goodness. Water in these areas are so hot, that it alters composition of rocks. The primary minerals are replaced by secondary minerals expressed by variety of colors and structures. One of the most beautiful features in these areas are formed by a process called sintering. It is manifested in the form of a thin crust of mineral salts and silica, accompanied by sulfur deposition. Moreover, yellowish green moss also can be seen along these hot areas. This is the only vegetation which can thrive above 35°C in this climate and soil type. If temperature drops below 27°C, grass will grow.