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Ice is slippery when it isn't too far below it's melting point because the surface molecules are less loosely bound than the bulk and form a thin liquid layer.

Pressure melting is a much smaller effect since it takes about 10 MPa of pressure per degree below freezing, which is more than ice skates can apply.

Presumably this "edge effect" isn't unique to water. Gallium at 20C (melting point about 30C) should also have such a surface layer. But most metals oxidize if exposed to air and/or water, forming an oxide layer which (for low-melting metals) melts at much higher temperatures. But if gallium at 20C is placed in argon and the oxide layer is removed, would the underlying metal feel slippery to a gloved hand?

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  • $\begingroup$ Gallium has a strong tendency to supercool, so... it would likely be fully liquid. $\endgroup$
    – Mithoron
    Commented Jul 11, 2023 at 22:29
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    $\begingroup$ @Mithron: If melted in the first place yes, but if it is warmed from a cold temperature or given a seed crystal it won't be liquid below 29.7C. $\endgroup$ Commented Jul 11, 2023 at 22:37
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    $\begingroup$ My instinct is that this surface disorder effect is more important for water than for gallium, since the water molecule and the way it packs is more complex than the gallium atoms. What this ultimately would entail, though, I don't know. Surface kinetics/thermodynamics sure can get messy... $\endgroup$ Commented Jul 12, 2023 at 11:40

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