Gneiss is formed when the minerals in granite (quartz, feldspar, mica, etc.) are rearranged into alternating bands of light and dark minerals.

Here's a breakdown:

* Original Granite: Granite is a coarse-grained igneous rock with a relatively even distribution of minerals.

* Metamorphism: When granite is subjected to intense heat and pressure (metamorphism), the minerals start to recrystallize and align themselves in specific directions.

* Banding: The light-colored minerals (quartz and feldspar) tend to align together, creating lighter bands. The darker minerals (mica, hornblende, etc.) form darker bands.

* Gneiss: The resulting rock, with its distinct banding, is called gneiss.

So, the answer is alternating bands of light and dark minerals.