Answer:
Quartz
Step-by-step explanation:
Gneiss is a form of metamorphic rock. It is characterized by its unique foliation, which shows alternating layers made of various minerals.
Gneiss is made up of majorly quartz and feldspar which are coarse in texture.
However, given the shiny and transparent features of quartz, it can be concluded that "Gneiss rocks contain QUARTZ which makes it shine.