The Differences Between Granite & Diorite

In the world of igneous rocks, diorite and granite are closely related. Each is hard, nonporous and found in similar areas of the world. To the untrained eye, the two can easily be mistaken; however, with a little information on the differences between these two igneous rocks, you can understand how they differ.

Granite is regularly used as a countertop.

Diorite and Granite Compositional Differences

Diorite is primarily composed of feldspar and various dark-colored minerals, which explains its black coloring. Granite is composed of four materials: feldspar, mica, quartz and hornblende minerals. These minerals themselves come in a variety of forms, giving granite a much larger variety than diorite.

Differences in Use: Antiquity and Modernity

Diorite has uses dating back to ancient times. Due it its sturdiness and hardness, diorite was used to carve the Code of Hammurabi. Diorite was also used as a fortification for walls and towers. Today diorite is used a stone slab for flooring and garden landscaping. In ancient times, granite was used for large-scale statues, and the Egyptians used it for constructing the Red Pyramid. Today, granite is used mostly for flooring and countertops.

Structural Differences

Granite has less density than diorite. Granite is a coarser-grained rock material. Both rocks are nonporous; however, granite is less porous, making it better suited for countertops and flooring. As diorite is denser, it weathers and lasts better in landscaping.

Other Differences

Availability is another differing factor of these two igneous rocks. Diorite is rarer than granite. Granite is often found on its own; for example, Georgia's Stone Mountain is one single granite outcropping. Diorite is usually only found alone in small tills. When found in larger quantities, it is usually found alongside granite and gabbro. Diorite is also a plutonic/intrusive igneous rock, meaning the minerals forming the rock crystallized prior to reaching the earth's surface. Granite is also a plutonic igneous rock; however, diorite forms at 200 degrees Celsius higher than granite, giving diorite less viscosity than granite. This means that granite is thicker and has higher levels of semi-fluidity due to the stone's internal friction.