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In the chemistry book that I'm reading, it says:

At even lower temperatures, the molecular movement becomes even more sluggish. The water molecules begin to align in a regularly repeating pattern, remaining in a fixed position relative to each other.

I have a few questions regarding that:

  1. Is there a case where, upon entering a solid state (I know that there's no fixed boundary to that state), the molecules form a completely chaotic structure in the entire volume, such that there will not be a repeated pattern in the structure?
  2. Does water molecules always form the same repeated structure upon entering solid state?
  3. How many solid state repeating structures/patterns are there - regarding water?
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    $\begingroup$ 1) Glasses are of that structure. 2) No. Snowflakes are a simple counterexample. 3) See phases of ice en.wikipedia.org/?title=Ice $\endgroup$
    – CuriousOne
    Commented Jun 25, 2015 at 7:56
  • $\begingroup$ @CuriousOne: a snowflake is still a single crystal (possibly with twinning) with the same crystal structure as other ice crystals. $\endgroup$ Commented Jun 25, 2015 at 9:12
  • $\begingroup$ @JohnRennie: A snowflake doesn't have translational symmetry. It is appealing to think that crystal growth is a simple process that causes a high level of order, but that's just not the case. $\endgroup$
    – CuriousOne
    Commented Jun 25, 2015 at 17:19

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There are two types of solid structures that aren't made of simple repeating units: glasses and quasicrystals.

When a crystal forms from a melt it requires the atoms/molecules in the melt to reoganise into the crystal structure. If the rate of solidification is fast enough the atoms/molecules don't have the time to reorganise and the solid formed is effectively a solid liquid with no long range order. The best known such material is glass, as used in windows, but many different amorphous solids are known. Ice can form an amorphous solid, though rather extreme cooling is required.

A quasicrystal is a solid that looks locally crystalline, but has no long range order so it can't simply be built from repeating units. In my days working in this area no examples of quasicrystals were known, though I note the Wikipedia article reports that real life quasicrystals have now been observed.

Your questions 2 & 3 are really part of the same question. Water forms many different types of crystal structure. Different structures are stable under different conditions i.e. different ranges of temperature and pressure. Under normal conditions ice always forms the structure known as Ice 1$_\text{h}$.

It isn't clear whether your question 3 is asking only how many different forms of ice there are (in which case see above) or whether you're asking more generally how many different types of crystal structures can exist. There are ony a finite number of possible crystal structures - in fact there are 230 possible structures. These are known as the crystal space groups. All crystals can be assigned to one of these groups.

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  • $\begingroup$ IIRC "Penrose Tiling" is the mathematical proof of quasicrystals, at least in 2 dimensions. $\endgroup$ Commented Jun 25, 2015 at 13:23

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