You are absolutely correct! Here's a breakdown of why igneous rocks that are dense and dark-colored form from magma rich in iron, magnesium, and poor in silica:

* Mafic Composition: These igneous rocks are classified as mafic, which means they are relatively high in magnesium (Mg) and iron (Fe).

* Low Silica Content: The term "mafic" itself comes from magnesium (magnesium) and ferric (iron). Mafic magmas have a lower silica (SiO2) content compared to other types of magma.

* Density and Color:

* Density: Iron and magnesium are denser than silica. This is why mafic rocks, with their high iron and magnesium content, are generally denser than other igneous rocks.

* Color: The presence of iron and magnesium contributes to the dark color of mafic rocks.

* Formation: Mafic magmas originate from deep within the Earth's mantle, where they are rich in iron and magnesium. These magmas often erupt as lava flows, forming dark-colored rocks like basalt and gabbro.

Examples of Mafic Igneous Rocks:

* Basalt: A common dark-colored, fine-grained volcanic rock.

* Gabbro: A coarse-grained, intrusive mafic rock.

* Diorite: An intermediate rock that bridges between mafic and felsic rocks (those rich in silica).

Let me know if you have any more questions!