Question

Granite, diorite, gabbro, and peridotite are ________ rocks.

1) metamorphic foliated
2) igneous extrusive
3) igneous intrusive
4) sedimentary clastic
5) sedimentary chemical and organic

Answer 1

Granite, diorite, gabbro, and peridotite are classified as igneous intrusive rocks, formed from the slow cooling and solidification of magma beneath the Earth's surface, resulting in a phaneritic texture.

Step-by-step explanation:

The student has inquired about the classification of rocks such as granite, diorite, gabbro, and peridotite. These rocks are all categorized as igneous intrusive rocks. This classification is based on the process by which they form. Igneous rocks are born from the cooling and solidification of magma below the Earth's surface. Because the cooling process occurs underground, it happens slowly, allowing the formation of large, visible crystals. This texture, known as phaneritic texture, is characteristic of intrusive rocks. Examples provided, such as granite and gabbro, are indeed intrusive igneous rocks with large grain sizes and generally composed of quartz, feldspar, and mafic minerals.Comparatively, metamorphic rocks, like gneiss, are formed by the transformation of pre-existing rocks under the influence of high pressure and temperature without the rock melting, which often results in a foliated texture. Sedimentary rocks form by the accumulation and cementation of mineral and organic particles, or the precipitation of minerals from solution. Neither metamorphic nor sedimentary processes apply to the rocks in question, making option 3, 'igneous intrusive,' the correct classification for granite, diorite, gabbro, and peridotite.