Shiny rock - ID request

[anonaddict]

ive encountered these shiny rocks and would like to find out what they are. like all other they are found on the beach near aarhus denmark and the scale is metric. ive tried my best to get closeups. unlike most shiny rocks i find, their refraction seems very colorful similar to how fish scales play in the light and show many different colors depending on the angle despite having a uniform color 

 

any information is welcome

[TqB]

Looks like schist, the fish scale effect being mica flakes.