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What is Feldspar?

Mary McMahon
Updated May 21, 2024
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Feldspar is a blanket term for a very large group of minerals that are extremely abundant on Earth. Around 60% of the Earth's crust is made up of these minerals, in fact, and they have numerous uses for humans, ranging from scouring solutions to glassware. Chances are that most people are probably looking at something which contains feldspar right now, although they may not be aware of this, since these minerals are so ubiquitous in the industrial world. Globally, the major commercial sources are Italy, Turkey, China, and Thailand.

The distinguishing feature of minerals in the feldspar group is that they are comprised of silicates of aluminum blended with other metals like potassium, calcium, sodium, and sometimes barium. The composition of an individual piece determines its chemical properties and what color it will be, but it shares similarities with other feldspars, like a crystalline structure. Before feldspar can be used in an industrial process, it must be profiled to determine its chemical composition, as different types will of course behave differently.

Many feldspars are formed in magma, crystallizing out as the magma cools, making them igneous rock. It also appears in the form of veins in other rocks, formed through processes of pressure, classifying it as a metamorphic rock as well. Feldspar sometimes occurs in sedimentary rocks also. Regardless as to the process which led to their formation, feldspathic rocks contain blocky crystals.

In the Earth, one of feldspar's important roles is in clay formation; as the material weathers, it turns into clays. Humans use it in pottery and glassmaking, and it is also added to scouring powders and used as a filler in a wide range of products. Some are quite attractive, leading people to use them as semi-precious gemstones, as they can polish up quite nicely, and feldspar is also used to make decorative accents on buildings and monuments. It can also be used to date various materials, using a variety of techniques depending on the type of mineral involved.

Many natural history museums keep several excellent examples of various types of feldspar in an array of colors and sizes. Examining such a display can give people a good idea of the diversity of this mineral group, which appears in the ground we walk on, the glasses we drink from, and in a large array of other materials as well, ranging from tile grout to toilets.

Frequently Asked Questions

What is feldspar and where is it commonly found?

Feldspar is a group of rock-forming minerals that make up about 41% of the Earth's continental crust by weight, according to the United States Geological Survey. It is commonly found in igneous, metamorphic, and sedimentary rocks, making it a significant component of both intrusive and extrusive rocks. Feldspar minerals are used in the manufacture of glass and ceramics.

How many types of feldspar are there and what are they?

There are two main types of feldspar, classified based on their chemical composition: plagioclase feldspar and alkali feldspar. Plagioclase feldspars contain calcium and sodium, while alkali feldspars contain potassium. These two groups encompass a variety of species such as orthoclase, microcline, and anorthite, each with unique properties and occurrences.

What are the distinguishing features of feldspar minerals?

Feldspar minerals are known for their distinct cleavage, breaking along flat planes, and for their hardness, which ranks about 6 on the Mohs scale. They often display a glassy luster and can be found in a range of colors, including white, pink, or gray. Their crystal structure is typically blocky or tabular, and they may exhibit striations on some cleavage surfaces.

What are the industrial uses of feldspar?

Feldspar is widely used in the industrial sector. It is a key ingredient in the manufacture of glass, where it acts as a flux to lower the melting temperature of quartz. In the ceramics industry, feldspar is used as a flux to improve the strength and durability of ceramic bodies. It's also used in paints, plastics, and rubber as a filler.

How is feldspar mined and processed?

Feldspar is typically extracted through open-pit mining, where the mineral is drilled, blasted, and then transported to a processing facility. Here, it is crushed, ground, and separated from other minerals by flotation or magnetic methods. The processed feldspar is then milled to a fine powder for various industrial applications.

Can feldspar be used as a gemstone?

Yes, certain varieties of feldspar are used as gemstones. The most well-known gemstone forms of feldspar are moonstone, sunstone, and labradorite, which are prized for their optical phenomena such as adularescence and labradorescence. These gem-quality feldspars are cut and polished for use in jewelry, showcasing their unique reflective properties and colors.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By riznyrauf — On Jun 19, 2012

What type of products can be made out of dolomite powder?

By anon222319 — On Oct 15, 2011

Does anyone know what type/kind of feldspar is used in scouring scrubs? Thank you, your help is much appreciated.

By hanley79 — On Jun 14, 2011

Feldspar is a very versatile material, and is used in a wide variety of products worldwide. Here in the United States where I live, over half of all feldspar in use goes to making glasswares, like dishes and windows and such.

The remaining amount goes into things like rubber and plastic, where the feldspar serves as an extender and filler. I would imagine the presence of feldspar in plastics and such might also help them to be more shiny, since it is a glass and mineral base with a nice shine to it.

While we're on a national viewing level of this stuff, let me note also that it might sound like there's tons of feldspar all around the planet for anybody who wants to collect some, but commercially, only a handful of countries mine it and sell it to the rest.

For example, in the year 2010 the vast majority of all commercially sold feldspar came from Italy, China and Turkey. I guess these countries are the most serious about mining feldspar, or perhaps have the best access to areas where mining it is easier.

Well, that and not all feldspar is the same. Since the term refers to a whole bunch of different minerals, I'm sure there are certain kinds of feldspar -- which China, Italy and Turkey may have better access to -- that are more desirable for the production uses that people have in mind than other types of feldspar.

The minerals themselves actually don't fascinate me as much as the production process. It's interesting how humans use and distribute natural resources among ourselves.

By TheGraham — On Jun 13, 2011

@Hawthorne - I've always wanted a rock tumbler, but I live in an apartment, and I hear that they are super noisy. Maybe I can convince my mom to let me run one at her house, which is in a rural area.

I had my doubts that it was worth the trouble and effort, but your glowing comments about how pretty rocks put through the tumbler look makes me more confident.

By the way, did you know that the word "feldspar" is originally based in German? "Feld" means "field", and "spar" is based on the word "spath", which roughly translates to more of an attribute than a word: "a rock that doesn't contain any ore".

Because the original second half of the word is "spath" instead of "spar", when somebody refers to a piece of mineral that contains feldspar, they call it "feldspathic". Isn't that fun?

I like geology, too, but I've never really studied it. I learned this stuff by reading books about quartz crystals, one of which mentioned feldspar quartz and made me go look up the word feldspar in several places. WiseGEEK's article explains nicely what feldspar is -- I knew it was in crystals, but I had no clue that it is also in clay.

By Hawthorne — On Jun 11, 2011

I first learned about what feldspar is in my geology class. I think it's neat how over half of the earth's crust is made of feldspar -- I'll bet most people in the world have had contact with some kind of feldspar, whether they know it or not!

I have a few pieces of feldspar minerals that I keep in my rock collection. Yes, rock collection -- I enjoy geology, what can I say? Even somebody who didn't would love the luster of certain crystals I have in my collection, polished and unpolished.

I like to put stones in a rock tumbler to polish them up if I'm going to be displaying them in my home. You can buy one for pretty cheap online -- trust me, it polishes up even pebbles from the yard into something pretty!

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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