What are some methods to obtain drinking water from a glacier or icefield, in the absence of snow or reachable meltwater? Collecting ice is much harder than collecting snow. Do I need to bring special tools or can I collect tools “in the wild” to break or scrape ice from a glacier/icefield for melting?
The Mohs hardness scale is a common scale used to describe the hardness (resistance to scratching) of different materials. The hardness of ice is between 1.5 and 6 Mohs. The hardness of granite is 7 Mohs so you should be able to scratch ice with rocks you find. I cannot find a definitive answer on the hardness of wood, but it seems like wood would not scratch steel (hardness of 4 Mohs) or even copper (hardness of 3 Mohs) so it is probably around a 3 or so. In a one off survival situation you can definitely pound on the ice with rocks to shatter manageable pieces. Using sticks will be a lot less efficient than rocks (and possibly not possible depending on temperature). If you need to gather a lot of ice, or do it regularly, a small hand drill and saw work well. An ice pick can also work. If you are going to try and shatter ice, you need to be careful to protect your eyes.
After obtaining manageable pieces, you are then left with melting the ice and warming the water. While you can do this with your own body heat, you need to be careful. You may be better off using the heat source to directly (or indirectly) melt the ice (e.g., by putting the hot pot directly on the glacier or pouring out hot/warm water).
Another answer talks about hardness. There is some relevance to that, but more importantly, ice is brittle, regardless of how hard it is. You don't need much of a tool to scrape or crack chunks from a large piece of ice like a glacier.
Also, any large piece of ice has to have edges someplace. It's easier to split off pot-sized chunks from edges than from a large flat plane of ice.
Another point is that very rarely do you have just pure clear ice in nature. I've been right up to a few glaciers, and they always were at least a little bit "snowy" on top. They aren't nice clear solid blocks of ice like ice cubes. You do see that when you go into a crevasse or under the glacier, but the surface is usually more like hardened snow than solid ice. It should not be hard to scrape some of that into a pot.
Yet another point, anywhere there are large ice features, like glaciers, there will be streams coming out the bottom end of them. If you can walk up to the foot of a glacier, you don't need to gather snow or chunks of ice at all. You just fill the pot with the inevitable meltwater flowing out. About the only time this doesn't work is in winter when the whole lot is covered with snow. But then you've got lots of snow to easily scoop up.
Quite often you'll have an ice axe with you in glacier country. That should be quite effective. If not, tent pegs, especially rock pegs or v pegs make decent chipping tools even for soft stone. You may need to hit them with a rock. Aluminium pegs are probably too soft; plastic ones definitely are.