If one imports only amssymb then \Diamond doesn't produce a WHITE DIAMOND like the one in the unicode.org character code charts. The glyph is rather small and looks more like LOZENGE. However, if latexsym is loaded, one gets a WHITE DIAMOND which looks like the one in the code charts, i.e., which actually is a square which sits on one of its vertices. One should note that the appearance of \Box also differs between amssymb and latexsym.
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