Why is biotite so shiny when sitting on the bottom of a shallow stream?

Question

This is a Geology question. Biotite is sometimes confused for gold. I need to know why.

Answer 1

Well , it's a mineral. Its normal color is black or brown, but when it's weathered (yes, in a shallow stream it can be weathered) then it will turn a shiny yellow color. Check out my source.

On the site: "Weathered tiny crystals of biotite can appear golden yellow with a nice sparkle producing a "fool's Gold" that has fooled many."

Answer 2

Biotite is normally in thin sheets (the molecules are that way) and when the water fills in the imperfections it looks like a perfect reflector.