The parent rock of biotite gneiss can be a variety of igneous or sedimentary rocks. Some of the most common parent rocks include:

* Granite: A common igneous rock with quartz, feldspar, and mica.

* Diorite: Another igneous rock with plagioclase feldspar and hornblende.

* Shale: A fine-grained sedimentary rock rich in clay minerals.

* Sandstone: A sedimentary rock composed of sand grains.

* Limestone: A sedimentary rock composed primarily of calcium carbonate.

The specific parent rock will depend on the specific composition and texture of the biotite gneiss. For instance, a gneiss rich in quartz and feldspar likely originated from a granite or diorite.

Key Point: The parent rock is transformed by heat, pressure, and/or fluids during the metamorphic process, leading to the development of new minerals and a distinctive foliation (banding) in the resulting gneiss.