Granite doesn't have a single crystal structure. It's a plutonic igneous rock, meaning it formed from magma cooling and solidifying deep underground. This slow cooling process allows for the formation of multiple different minerals, each with its own crystal structure.

Here's a breakdown:

* Quartz: Quartz is a common component of granite and has a trigonal crystal system.

* Feldspar: Feldspar (both plagioclase and orthoclase) are abundant in granite and have a monoclinic or triclinic crystal system (depending on the specific feldspar).

* Micas: Biotite and muscovite, the mica minerals found in granite, have a monoclinic crystal system.

* Other minerals: Granite can contain various other minerals, like hornblende, garnet, or zircon, each with their own crystal systems.

Therefore, granite is not a single crystal, but rather an aggregate of various mineral crystals intergrown together. It's this complex interplay of different crystal structures and mineral compositions that gives granite its unique appearance and characteristics.