Ice

Ice is the third state of aggregation of water and forms at normal pressure, presence of crystallization nuclei and a temperature lower than 0 °C. As a naturally occurring crystalline solid with a defined chemical composition, ice belongs to the minerals. Due to its chemical structure H2O, ice belongs to the substance group of oxides.

Ice crystallizes in the hexagonal crystal system and occurs in nature in various forms, from snowflakes to hailstones and the frozen surface of mostly stagnant waters to glaciers. Its density of 0.918 g/cm³ (pure, air-free ice at 0 °C) is lower than that of water (1 g/cm³). Due to this density anomaly, ice floats on the water surface and forms ice sheets, ice floes and icebergs. About 90 percent by volume of the ice is under water (buoyancy force of the water versus weight force of the ice) and only about 10 percent by volume is above the water surface.

In its pure form, ice consists of colourless, transparent crystals. However, blocks of ice usually contain many fine air bubbles trapped during the solidification of the ice crystals and therefore appear white due to multiple refraction of light. As a chemical substance, it is characterized by some special properties based on the anomalies of water.

Ice plays an important role in numerous meteorological phenomena. The ice caps of the polar regions are of great importance for the global climate and especially for the global water cycle. It therefore also has a correspondingly decisive influence on our biosphere.

The science of forms, occurrence and properties of ice and snow is called glaciology.

Etymology and history

The etymology of ice can be traced back via the Old High German, Middle High German and Low German 'îs' to the Germanic 'īsa'. Through diphthongization (sound change from one to two vowels), this original word became, among others, the German Eis and the English ice.

However, ice only appeared as an independent type of mineral at the beginning of the 19th century. Before that, it (including water, snow and hail) had been considered one of the four basic elements since antiquity, along with fire, air and earth, and even in the systematics of Abraham Gottlob Werner, ice was not listed until the last edition in 1817 (1st edition 1787).

Only Friedrich Hausmanns describes water or its different solid forms (varieties) in his Handbuch der Mineralogie of 1813 as a mineral, classified in the second class of the "incombustibles" and the second order of the "oxydoids". According to Hausmann, ice and snow belong to the "soft water", which occurs tabularly as ice floes, stalactitically as icicles, bark-like as black ice and spheroidally as hail.

Classification

Already in the outdated 8th edition of the mineral systematics according to Strunz, ice belonged to the class of "Oxides and Hydroxides" and there to the division of "Compounds with M2O and MO", where it formed the unnamed group IV/A.01 as ice (I) together with ice (Ic). In the Lapis mineral directory according to Stefan Weiß, which was last revised and updated in 2018 and which, out of consideration for private collectors and institutional collections, still follows this classical systematics of Karl Hugo Strunz, the mineral received the system and mineral no. IV/A.01-10. In the "Lapis systematics" this corresponds to the division "Oxides with the ratio metal : oxygen = 1 : 1 and 2 : 1 (M2O,MO)", where ice, as the only member, forms an independent but unnamed group.

The 9th edition of Strunz's mineral system, valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, also classifies ice in the division of "Oxides with the molar ratio metal : oxygen = 2 : 1 and 1 : 1". However, this is further subdivided according to the exact anion-cation ratio and the relative size of the cations, so that the mineral can be found according to its composition in the subdivision "Cation : Anion (M : O) = 2 : 1 (and 1.8 : 1)", where it forms the unnamed group 4.AA.05 as ice-Ih together with ice-Ic.

The system of minerals according to Dana, which is predominantly used in English-speaking countries, also classifies ice in the class of "oxides and hydroxides" and there in the division of "oxides". Here it is the only member of the unnamed group 04.01.02 within the subdivision "Simple oxides with a cation charge of 1+ (_A2O)".