What rock type is primarily located on the plains of the moon?

The primary rock type located on the plains of the moon is basalt. This volcanic rock forms from the solidification of lava and is typically dark in color. The lunar maria, or the large, dark plains on the Moon's surface, are primarily composed of basalt that erupted from volcanic activity billions of years ago.

Basalt is significant in terms of lunar geology because it is a product of the Moon's ancient volcanic processes, which created these expansive flat regions known for their relatively low crater density when compared to the highlands. The basalt on the Moon is rich in iron and magnesium, which gives it its characteristic black color and contributes to the lower reflectivity of the lunar maria compared to the lighter highlands, which are composed mainly of anorthosite.

In comparison, anorthosite is more abundant in the highland regions and is not representative of the lunar plains. While "lunar rocks" could refer to any rock types found on the Moon, it does not specifically identify the dominant type found on the plains. Natural glass, formed from rapid cooling of volcanic materials, is much less common and not the primary composition of the plains. Thus, basalt stands out as the correct choice.