Final answer:
Igneous rocks containing 70% to 77% silica are typically considered felsic rocks and are composed of feldspar, quartz, along with minor hornblende and biotite. These characteristics fit with coarse-grained intrusive rocks.
Step-by-step explanation:
The classification of igneous rocks is often based on their mineral composition, specifically silica content, and their texture. Rocks with 70% to 77% silica content typically fall into the category of felsic rocks, which are rich in feldspar and quartz. These minerals, often along with minor amounts of hornblende and biotite, comprise coarse-grained intrusions in igneous rocks.
According to the classification chart based on mineral content and identifying characteristics, felsic igneous rocks (rich in quartz and feldspar) such as granite would likely contain this higher amount of silica. Porphyritic textures feature large crystals set in a finer-grained matrix, indicating a complex cooling history but are not directly indicative of silica content.