I did not include in my last email, in the table of hardnesses, any figures for ice. So, a little more research, and here it is:-

http://www1.lsbu.ac.uk/water/hexagonal_ice.html

(there are many different forms of water ice; this is info on hexagonal ice)

Here is the relevant quote:

The hardness of ice varies with the temperature, increasing from about or below that of gypsum (≤2 on Mohs scale) at 0 °C to about that of feldspar (6 on Mohs scale) at -80 °C, an anomalously large change in absolute hardness (>24 times) with temperature.

The Mohs scale is yet another measure of hardness (in use since 1822) but is not linear. Here is the scale:

http://www.gordonengland.co.uk/hardness/mohs.htm

This is based on “who can scratch who?”. So, Corundum can scratch Topaz, but cannot scratch Diamond. Very understandable, but not scientific in terms of SI units (which is what ‘MPa’ are).

Here’s some SI info from a scientific paper on ice:-

http://www.bjerkas.info/Papers/Mech prop.pdf

MECHANICAL PROPERTIES OF ICE RIDGES AND LEVEL ICE, IN-SITU AND LABORATORY TESTING 2003

ABSTRACT

Ice has been sampled from first-year sea ice ridges and level ice both in the Van Mijen fjord in Svalbard and in the North-western Barents Sea.

The average unconfined strength for vertical samples was 6.0 MPa for the level ice, 5.0 MPa for the consolidated layer and 3.3 MPa for the rubble. The hardness was clearly dependent on the temperature, and it varied from 11 to 37 MPa

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Alex Kemp