Up until 1964, they were 90% silver. Since 1965, though, they've been comprised of two layers: an inner core of copper clad with an outer layer of cupro-nickel (75% copper and 25% nickel). Overall, this makes the coins 8.33% nickel and 91.67% copper. By metal content value, the current coins are worth a whole lot less than a "real" pre-1965 quarter.

Portions of a whole. Or, metal. Depends on what you're asking.

A blend of different metals

"quarters" of what ?