WW
Sorry I didn't rsvp IMMEDIATELY, but I spent the last couple of days earning my keep, to-ing and fro-ing from a mine site near Mt Magnet, about 600km N of Perth (in the middle of nowhere).
Interesting q about the SG of ice. You are quite correct that, because it floats on water, it is less dense / has a lower SG than water. What that value is I don't know - haven't had time to look it up.
Why is it so?
When water is frozen it expands - or, in scientific terms, its volume increases. Thus, a volume of ice (say one cc) will, when thawed, produce less than one cc of water. SG is calculated as the mass (or "weight" - to use the incorrect vernacular) of a substance per standard unit of volume (one cc). Thus it's easy to see that a cc of ice has less mass than the same volume of water, a lower SG and that it will float. well I think I can follow all that!!
A WILD stab as to what ice's SG is.....considering that seven eighths of an iceberg sinks in sea water (which is denser than pure water), it is tempting to assume that the SG of ice is around 12.5% less than that of water - ie 0.875. Evenkite, the candidate for lowest SG last week, has an SG of 0.87 so it would be a close call if these wild assumptions are anywhere near correct. If I knew what the coefficient of expansion (ie the volume change) for the freezing of water was we'd have the answer!
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