Ice is water frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaque bluish-white color. In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects. Beyond the Solar System, it occurs as interstellar ice. It is abundant on Earth's surface particularly in the polar regions and above the snow line and, as a common form of precipitation and deposition, plays a key role in Earth's water cycle and climate. It falls as snowflakes and hail or occurs as frost, icicles or ice spikes and aggregates from snow as glaciers and ice sheets. Ice exhibits at least eighteen phases (packing geometries), depending on temperature and pressure. When water is cooled rapidly (quenching), up to three types of amorphous ice can form depending on its history of pressure and temperature. When cooled slowly, correlated proton tunneling occurs below 253. 15 C (20 K, 423. 67 F) giving rise to macroscopic quantum phenomena. Virtually all ice on Earth's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih (spoken as 'ice one h') with minute traces of cubic ice, denoted as ice Ic and, more recently found, Ice VII inclusions in diamonds.