Random Riddle: An Altered State - Common Sense Evaluation

Over time, in a dark place I’m formed
I prevent my surroundings from being warmed

Once deposited, if long enough you wait
I remain, but in an altered state

With my kind, you fill a plastic chest
Chilling during a summer picnic rest

One more thing I’d like to mention
My name suggests a third dimension

What am I?

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