Diorite: Coarse-Grained Intermediate Rock

Being of intermediate composition between felsic and mafic, diorite is classically a salt and pepper rock made largely of white to light gray plagioclase and black hornblende. Some diorites contain biotite as well as hornblende, and some contain up to 10% quartz. If you have more than 10% quartz, you probably have a granite on your hands. If you clearly have abundant K-feldspar, you probably have a granite on your hands.

You can see that this rock has roughly an equal abundance of white and black minerals.

If you click to zoom, you will see only one feldspar and no quartz. It is tough to identify the minerals from the photo, but in person they appear to be plagioclase and hornblende.

This diorite is more salt than pepper, but it appears to have less than 10% quartz and no K-feldspar. It thus qualifies as a diorite.
This diorite is closer to the classic balance of mafic and felsic minerals (salt-and-pepper appearance). Unfortunately, I have no super close-up for you.

Go back to Igneous Rocks page

Return to Image Home

E-mail C.E.Jones with comments or corrections. Delete "ALLCAPS" from address before sending.
Geology and Planetary Science Home Page