Re: Is glacial ice harded then regular 'man made' ice?

I am not sure how to answer your question. Blue glacial ice has a density of about 900 kg/m3 (from How Glaciers Form and Flow). Oddly, this value is actually lower than the typically quoted density of ice at 917 kg/m3 (water has a density of ~1000 kg/m3). Typically, more dense materials are "harder" (the best example is the difference between graphite and diamonds), which would suggest that glacial ice is "softer" than regular ice cubes, probably because glacial ice still has air trapped in it from when it used to be snow flakes. Glacial ice starts out as snow and is transformed into blue ice by high pressure from the weight of the cumulative snow layers above.

So, more dense means that regular ice cubes will last longer, but how much longer will depend on the exact conditions under which you are trying to melt each... you'll have to figure that one out on your own by finding the heat transfer coefficient of ice and glacial ice or by doing some experiments.

The USGS's Coastal & Marine Geology Program has some good information on Glacier FAQs and Myths that might be of interest, including their answer to the question "Doesn't glacier ice last longer in drinks?"

So, thanks for your question! And stay cool this summer...

Kieran