In fact, the large mineral crystals of intrusive igneous rocks can be seen without a lens or microscope. They are often coarse textured and have a rough feel, unlike extrusive rocks, which feel smooth. One type of intrusive igneous rock that forms from the same type of magma as basalt is called gabbro. Gabbro contains no quartz. Rather, it is a mafic rock whose main mineral constituents are pyroxene, feldspar, and some olivine.
Granite is made up primarily of quartz, mica and feldspar.
The best known of the igneous rocks is granite, an intrusive rock that forms from the same type of magma as rhyolite. Like rhyolite, granite is a felsic rock, and is composed almost entirely of feldspar and quartz. But unlike rhyolite, granite is rough textured and has obvious crystals. In certain cases where the granite forms very slowly, crystals can be up to several feet long. Because granite is a hard and tough rock, it is used for many construction projects.