Here's one for the scientists:

I am writing a mystery in which the murder victim is encased in an ice coffin and dumped in a lake. Here's what I would like to have happen, but I need to know whether it is feasible:

The coffin melts overnight and in the morning a tramp fishes a wallet out of the lake and his hand bumps against a fist-sized lump of the ice. He takes it out, thinking it's a diamond, and the story goes on from there.

The novel is set in Texas and it can be any time of year.

Thermodynamics anyone? How long does an ice coffin take to melt down to one lump, and what time of year would it need to be?