En grammar, a clause and a phrase are both parts of a sentence but a clause is considered a grouping of words which contain both a subject and a verb. A phrase on the other hand is a grouping of words that does not contain a subject and a verb.
In the example given above, the phrase, 'The solid portion of a comet', although it contains a subject, it lacks a verb, therefore it is not a clause.
Ponyboy suggests that the main difference was "money that separated us", but Cherry also thought that there was something more that made the groups different(38). According to Cherry Valance, the main dividing factor was how the two groups dealt with their emotions: "You greasers have a different set of values.