What Is the Most Common Mineral?

Depending on how the question is worded, the answer could be quartz, feldspar, or bridgmanite. It all depends on how we classify minerals and what part of the Earth we're talking about. 

Most Common Mineral of the Continents

The most common mineral of the Earth's continents—the part of the world that where humans dwell—is quartz, the mineral SiO₂. Nearly all the sand in sandstone, in the deserts of the world, and on the world's riverbeds and beaches is quartz. Quartz is also the most common mineral in granite and gneiss, which make up the majority of the deep continental crust. 

Most Common Mineral of the Crust

Feldspar is called a group of minerals only for the convenience of geologists. The seven major feldspars blend smoothly into each other, and their boundaries are arbitrary. Saying "feldspar" is like saying "chocolate-chip cookies," because the name embraces a range of recipes. If you consider it as one mineral, feldspar is the most common mineral on earth, and quartz is the second most common. This is especially true when you consider the whole crust (continental plus oceanic).

In chemical terms, feldspar is XZ₄O_8, where X is a mixture of K, Ca, and Na, and Z is a mixture of Si and Al. To the average person, even the average rockhound, feldspar looks pretty much the same no matter where it falls in that range. Also, consider that the rocks of the seafloor, the oceanic crust, have almost no quartz at all but abundant amounts of feldspar. So in the Earth's crust, feldspar is the most common mineral. 

Most Common Mineral of Earth

The thin, rocky crust makes up only a small portion of the Earth—it occupies just 1% of its total volume and 0.5% of its total mass. Underneath the crust, a layer of hot, solid rock known as the mantle makes up about 84% of the total volume and 67% of the total mass of the planet. The Earth's core, which accounts for 16% of its total volume and 32.5% of its total mass, is liquid iron and nickel, which are elements and not minerals.

Drilling past the crust presents major difficulties, so geologists study how seismic waves behave in the mantle in order to understand its composition. These seismic studies show that the mantle itself is divided into several layers, the largest of which is the lower mantle.

The lower mantle ranges from 660 to 2700 km in depth and accounts for roughly half of the planet's volume. This layer is made up mostly of the mineral bridgmanite, a very dense magnesium iron silicate with the formula (Mg,Fe)SiO₃. 

Bridgmanite makes up around 38% of the planet's total volume, meaning it is by far the most abundant mineral on Earth. Although scientists have known about its existence for years, they had not been able to observe, analyze, or name the mineral because it does not (and can not) rise from the depths of the lower mantle to the surface of the Earth. It was historically referred to as perovskite, as the International Mineralogical Association does not allow formal names for minerals unless they have been examined in person.

That all changed in 2014 when mineralogists found bridgmanite in a meteorite that had crashed into Australia in 1879. During impact, the meteorite was subjected to temperatures in excess of 3600 degrees F and pressures around 24 gigapascal, similar to what is found in the lower mantle. Bridgmanite was named in honor of Percy Bridgman, who won a Nobel Prize in 1946 for his research of materials at very high pressures.

Your Answer Is...

If asked this question on a quiz or test, make sure to look carefully at the wording before answering (and be prepared to argue). If you see the words "continent" or "continental crust" in the question, then your answer is most likely quartz. If you just see the word "crust," then the answer is probably feldspar. If the question does not mention the crust at all, go with bridgmanite.