All About Diorite – Uses, Properties, Color, and Worth

Diorite is a very hard intrusive igneous rock made of silicate type minerals. The minerals in diorite will mainly be plagioclase feldspar and in lesser amounts hornblende, biotite, and pyroxene.  Diorite is considered an intermediate rock, which means it ranges in elemental composition.  

The chemical composition of intermediate rocks such as diorite will range from magnesium and iron (mafic), to elements that form feldspar and quartz (felsic)

Diorite will consist mostly of what is known as plagioclase, a very sodium rich group of feldspar minerals.   At one end of the spectrum of plagioclase you will have a high concentration of albite, at the other end you will have a high concentration of anorthite.  Diorite will typically fall in-between this range with a concentration of 70-50% albite with a 30-50% of anorthite, which is known as andesine in the plagioclase group of minerals.

When identifying diorite rock you can look for what is called the “salt and pepper” look.  The contrast of very white and very dark course minerals will help with identifying diorite.

To better identify diorite, see my article “The Best Ways to Visually Identify Diorite“

Diorite is considered a phaneritic intrusive igneous rock. Phaneritic means that diorite contains crystals that are large enough to see with the naked eye.

Diorite texture will often depend on the grain sizes available in the rock. Typically the texture will be fairly course unless diorite is smoothed out and polished.

Diorite Color

The color of diorite will range in many different grays to black with white.  Diorite’s color will not be one solid color, but more of a speckled effect of white, off whites, to grays, to black.  This speckled effect has commonly been called the “salt and pepper” look.

Diorite Uses

Diorite is used in roads and pavement, as well as other structural building materials due to its durability.  Diorite can also be used as a more cosmetic type of building stone that you might find in parks, curbs, or outside of buildings…

Part of that beautiful cosmetic look we commonly see with diorite is in the application of shinny polished countertops.  Diorite or granite, most of the time people will call all countertops “granite”, even if it is diorite. This helps avoid potential confusion in identifying the rock it was made from. 

In history we find that diorite sculptures, statues, and other items were carved from diorite due to its durability and ability to take a nice polish.  Ancient Inca and Mayan civilizations would use diorite for walls. From previous history, you can still see the remnants of diorite cobblestone streets found in various parts of the world.

Though diorite is not very rare, most historic applications of its use were due to the availability of the rock in the near area.  

Diorite jewelry is another use that may not be so commonly known. As pendants, rings, or earrings, diorite will need to have some pretty intricate patterns to outperform the eye appeal of many other rocks and minerals.

Diorite Worth and Value

The worth of diorite will be small but can increase due to what form it takes.  When in the form of crushed diorite stone for building material, the worth will be around $20 to $50 per yard.  When in the form for some sort of cosmetic appeal such as a countertop, you can expect $40 to $80 per square foot.

For the example of the diorite countertop, or granite countertop for those that like the sound of that better.  Since it is cut and polished, a diorite countertop will cost you thousands depending on the surface area you wish to cover.

These cosmetic applications of diorite will be from diorite rock that had more time to crystalize. This gives better eye appeal, so always expect nicer looking diorite to pull in more of a price.

Diorite Formation

Diorite rock is formed by the mixing of magma containing minerals that make up rocks like basalt, gabbro, and granite. This mixing of two magmas will create the intermediate composition that comprises diorite.  To finish it off, a little bit of crystallization underground will give it that sparkle. 

Diorite and Andesite

Diorite and Andesite have pretty much the same chemical composition.  However, the reason why diorite and andesite look so different is because both these igneous rocks did not crystalize the same way. 

Diorite is an intrusive igneous rock. It spent more time down under the earth cooling off more slowly, allowing crystallization to occur.  This makes the grain size of diorite larger. This allows you to easily see the contrast of the darker and lighter elements.

Andesite did its cooling off on or near the surface of the earth, making it an extrusive igneous rock.  The quicker cooling process of an extrusive igneous rock does not allow for much crystallization. This makes andesite have a smaller grain size giving it a very different look than diorite.

Diorite and andesite are examples of igneous rocks. I have written an article with some great information on igneous rocks “What are Igneous Rocks – Intrusive and Extrusive“. This article will go into more detail about igneous rocks and the two types of igneous rocks, intrusive and extrusive.