Pyrite is the classic "Fool's Gold" . There are other shiny brassy yellow minerals, but pyrite is by far the most common and the most often mistake for gold .  Whether it is the golden look or something else, pyrite is a favorite among rock collectors. It can have a beautiful luster and interesting crystals.
It is so common in the earth's crust that it is found in almost every possible environment, hence it has a vast  number of forms and varieties.

Bravo rite is the name given to a nickel rich sulfide. It is closely related to pyrite but contains up to 20%  nickel. Some mineral books treat it as a variety of pyrite.

Pyrite is a polymorph of marquisette, which means that it has the same chemistry, FeS2, as marcasite;
but a different structure and therefore different symmetry and crystal shapes. Pyrite is a difficult to distinguish from marcasite when a lack of clear indicators exist.
 

Here are some other good sites:
Rocks
Mineral Display
 
 
 

by:Stephen Pike