Question

Would you expect extrusive rocks produced by an explosive volcano to be light or dark in color?

1) Light
2) Dark

Answer 1

Extrusive rocks produced by an explosive volcano are generally expected to be light in color due to their rapid cooling and the presence of light-colored felsic minerals such as quartz and feldspar, which are typical in rocks like tuff and rhyolite.

"The correct option is approximately option 1"

Step-by-step explanation:

Based on the information provided about volcanic fragmental rocks and igneous rocks, we can determine the expected color of extrusive rocks produced by an explosive volcano. Explosive eruptions produce solid fragments and ash, often resulting in rocks such as tuff, which is described as light colored and sometimes contains glass and pumice fragments. Tuff may appear similar to rhyolite, which is a felsic extrusive igneous rock with a light gray to pinkish color.

Rhyolite is significant in this context due to its composition and formation process; it is very finely crystalline because it cools from a high-viscosity lava, which does not allow large crystals to form. With the rapid cooling rates of lava upon eruption, the resulting extrusive igneous rocks are fine-grained and often light in color due to the presence of minerals like quartz and feldspar, which are typically lighter in color than the mafic (dark-colored, iron and magnesium-rich) minerals.

Therefore, we would expect extrusive rocks produced by an explosive volcano to be generally light in color, as evidenced by rocks like tuff and rhyolite. Light coloration indicates a higher silica content, typical of felsic rocks, which are associated with more explosive volcanic activity.

This characteristic is opposed to the dark-colored basalts that tend to form from less explosive eruptions and have a higher content of mafic minerals.

Answer 2

Extrusive rocks produced by an explosive volcano are likely to be light in color due to the presence of felsic minerals like quartz and feldspar in rocks such as rhyolite. The correct option in the final answer is 1) Light.

Step-by-step explanation:

When considering the coloration of extrusive rocks produced by an explosive volcano, it is important to understand how these rocks form and the minerals they contain. The formation of volcanic fragmental rocks, such as tuff, involves explosive eruptions that eject solid fragments and ash. A notable type of extrusive igneous rock is rhyolite, which, similar to granite in composition, tends to be light in color due to the presence of felsic minerals like quartz and feldspar. As for the texture, these rocks are aphanitic (very finely crystalline) since they rapidly cool on the Earth's surface, which does not allow for large crystal formation.

Variations in the chemical composition and mineral content of the magma determine the rock's color. Therefore, the light coloration of rhyolite and similar rocks can be attributed to their high silica content and the predominance of felsic minerals, which typically lead to a lighter color. In contrast, mafic rocks with minerals rich in iron and magnesium, such as basalt, exhibit a darker coloration. Given that rhyolite is mentioned as a light colored volcanic rock, we can infer that extrusive rocks produced by an explosive volcano would more likely be light in color. In summary, the correct option in the final answer is 1) Light. This is supported by the presence of light-colored minerals and the typical coloration of rhyolite, a representative example of an extrusive rock formed in such explosive volcanic events.