I was just thinking earlier today that water ice could use an overhaul similar to what geology got while browsing through the wikipedia article in a fit of boredom.
For example, on glaciers, snow tends to undergo similar changes--analogous, not exactly--that sediments do (deposits -> sedimentary -> metamorphic) only on a faster time scale. It'd be pretty awesome to dig into a glacier, loose snow on top as it is now, a layer of
névé below it followed by a layer of
firn and finally glacial ice down to the rock. Névé and Firn are white, glacial ice would be the traditional blue.
If it could eventually be managed, it would be further awesome if snow fall could be converted to new walls of ice, and the wall below it into the next stage. If you were not careful, it would be possible to get your glacier fort buried in ice. I believe this has been suggested before, though.
Also, some random cosmetic features like
ice needles and
frost flowers--which also come in frost
beard varieties, see the images in the article. Frost flowers and ice needles form when the air is below freezing, but a plant or the soil, respectively, is not. The cold air basically wicks water out to where it freezes into long thin structures.
They would occur in cold biomes. Have them spawn during spring/fall (think spider webs), and melt by day or break when pathed over. A dwarf lucky enough to notice one would get a happy thought: "Admired a lovely frost flower recently." Possibly an unhappy thought if a dwarf notices he broke one: "Has accidentally destroyed a frost flower lately." Perhaps not... sparking a tantrum spiral because Urist McClumsyyetattentive broke a bit of frost is... "
Slept uneasily due to noise lately. Has witnessed death. Has accidentally destroyed a frost flower lately."
In seas and lakes, when it's very cold but not enough to solidify the body,
frazil ice and
ice discs could be implemented as contaminants on the surface (that don't affect the water quality like real contaminants do).
Anchor ice could also be spawned on the bottom of the body of water.