Here's why:

* Streak is the color of a mineral's powder. It's determined by rubbing the mineral against a streak plate (unglazed porcelain tile).

* Andesite is a volcanic rock, primarily composed of plagioclase feldspar, pyroxene, and amphibole. These minerals are generally light in color.

While andesite itself doesn't have a defined streak, its constituent minerals generally produce a white to gray streak when rubbed on a streak plate.