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Ice largely exists, or at the least, existed, to be the special version of Rock.
Both are great offensively. Both are poor defensively. Both are broadly presented as thematically slow. Both have weather that causes gradual HP loss.
In Gen 1, most were saddled with another type (Ice/Water and Rock/Ground). In Gen 1, most were slow, bulky, and strong in their particular damage type (special vs physical).