Fool's Gold can be one of three minerals. The most common mineral mistaken for gold is pyrite.
A naturally occurring inorganic element or compound having an orderly internal structure and characteristic chemical composition, crystal form, and physical properties.
Gneiss is a coarse-grained, foliated metamorphic rock that commonly has alternating bands of light and dark-colored minerals.
Sterling silver is the standard of quality for articles containing 92.5% silver and 7.5% copper (and/or other alloys).
The fineness of jewelry gold is stated as the number of parts in twenty-four that are gold. Thus, 24 karat gold is pure gold; 12 K would be an alloy that is half gold and half copper or other metals.
White gold was originally developed to imitate platinum, and is usually an alloy containing 25% nickel and zinc. If stamped 18 karat, it would be 75% pure gold.
A rock is an aggregate of one or more minerals; or a body of undifferentiated mineral matter.