Which of the following is not an igneous rock ?

Question

Accepted Answer

Geyserite is not an igneous rock because it is a type of opaline silica that precipitates from the hot spring or geyser water. It's a chemical sedimentary rock, formed by the deposition of minerals from solution.

Here's why the other options are incorrect:

*   **Pegmatite:** Pegmatite *is* an igneous rock. It's a very coarse-grained intrusive igneous rock, formed during the late stages of magma crystallization.

*   **Tuff:** Tuff *is* an igneous rock. It's a type of volcanic rock made of consolidated volcanic ash.

*   **Gabbro:** Gabbro *is* an igneous rock. It's a coarse-grained, dark-colored, intrusive igneous rock chemically equivalent to basalt.