# Nomenclature for different types of ice

How many types of ice exist and what is their nomenclature? I know that the ice on Earth is $I_h$, but why so?

• You can have a look at the phase diagram of water provided in this answer. There you can see which types of ice exist under different conditions. Nov 26, 2014 at 13:44

## 2 Answers

The first thing to note about ice water is:

All ice is not crystalline and not all crystalline water is ice

There appear to be fifteen crystalline phases of ice, named 'Ice 1' to 'Ice 15' using Roman numerals $I$ to $XV$. There also appears to be three 'polyamorphic' states:.

$LDA$ : Low Density Amorphous

$HDA$ : High Density Amorphous

$VHDA$ : Very High Density Amorphous

All crystalline ice is tetrahedrically coordinated (where the oxygen atoms are in fixed positions relative to each other but the hydrogen atoms may or may not be disordered but obeying the 'ice rules'), and the polymorphs differ primarily in H-bond angles and next-nearest neighbour separations.

Ice I encompasses all ice found on naturally on earth (in a stable form).

This is usually split into two phases called $I_h$ and $I_c$.

Hexagonal ice (ice $I_h$) is 'ordinary ice', the form of all natural snow and ice on Earth. This is evidenced in the six-fold symmetry in ice crystals grown from water vapor (that is, snow flakes).

Cubic ice (ice $I_c$) is a solid form of water that can form in high clouds. Ice Ic is metastable, and irreversibly converts to ice $I_h$. Both forms contain similar layers of hexagonal rings, but differs in the way these layers are connected.

For more information on their structure and properties of ice, check out 'the Many Phases of Ice'.

Martin Chaplin maintains a fairly thorough and well referenced online resource on water, which includes a comprehensive section on the ice phases.

Finally, Google Books has the definitive 'the Physics of Ice' by Petrenko & Whitworth available online.

• I see there few forms of ice for each amorphous state, so there are even more than 20 forms of ice, right?
– EJC
Nov 26, 2014 at 16:46
• That depends on how you want to distinguish one form of ice from another (crystal structure, symmetry or density) and on how 'stable' (or 'metastable') the form in question is. The resources described at the end of my answer give more details.
– theo
Nov 26, 2014 at 17:03

There are different types of ice, depending on its cristalline structure.

My guess would be that Ice $I_h$ and $I_c$ are named directly after their structure, which is respectively hexagonal and cubic.

The numbering, which makes Ice I, Ice II, Ice III and so on till Ice XV, seems to be arbitrary, probably ordered in sequence as they have been discovered. This also tells you about the number of different types of ice known: 16 (or 19 if we considering amorphous ice in its three forms).

• Isn't it 19 then?
– EJC
Nov 26, 2014 at 16:23
• Yes, sorry. Miscalculation. :) Nov 26, 2014 at 16:27