Feldspar vs Quartz: What Are They, And What's The Difference?

If you’re new to rockhounding, it can be pretty easy to mistake feldspar for quartz and quartz for feldspar.

However, once you know a little bit more about them, it’s not too hard to spot the differences and discern which mineral is which.

This article will explain what each mineral is, where to find them, and how they are different and similar to one another.

Feldspar vs Quartz: Explained

First, let’s look at what they are.

Feldspar Facts

Feldspar isn’t actually one individual mineral, but a group of minerals with such similar structures, chemical compositions, and physical properties that they’re just classified as feldspar.

There are just about 26 different minerals that fall into this classification, and these are grouped into two subgroups.

The first is plagioclase feldspar.

The minerals in this group contain calcium and sodium, and are a combination of albite and anorthite.

Some of the better known minerals in this category are labradorite, albite, and andesine.

The second subgroup is potassium feldspar, which, obviously, contains potassium.

The minerals in this group are made from the same compounds but have different crystal structures.

Some of the better known potassium feldspar minerals are anorthoclase, sanidine, and microcline.

Even though these two subgroups of feldspar are different, they’re similar enough to be grouped together.

While feldspar isn’t known for its appearance, occasionally the right circumstances can occur to render feldspar’s appearance gorgeous enough to be considered a gemstone.

Feldspar gemstones include moonstones, sunstones, aventurine, and amazonite.

Other than those rare exceptions, feldspar is most often white, though the exact chemical compounds that make it up can make it appear blue, brown, gray, orange, green, pink, yellow, or colorless.

Feldspar is also a very common mineral with many uses.

It is often crushed into a powder and then used to make glass, ceramics, pottery, paint, and plastic.

Quartz Facts

Quartz, on the other hand, is the most abundant individual mineral found on earth.

All variations of quartz have the same chemical formula, but form under vastly different circumstances, which makes each variation unique and often colorful.

Some of the more well-known variations of quartz include jasper, amethyst, rose quartz, milky quartz, and smokey quartz.

Quartz is much more highly sought after for its appearance, and many quartz variations qualify as gemstones because of their beauty and any impurities in the rock which make them rare.

Because of its abundance, strength, and heat-resistance, quartz is often used in manufacturing electronics, abrasives, glass, hydraulic fracturing, and more.

Similarities Between Feldspar and Quartz

While feldspar and quartz are often mistaken for each other, there are really only a few similarities.

First, the minerals overlap in color, and both can be found in many different colors and levels of opaqueness.

They’re both also silicates, which simply means that their chemical compositions include silicon.

And lastly, both minerals are often found in the same rocks.

Differences Between Feldspar and Quartz

The most significant difference to note between these two minerals is that feldspar is a group of minerals, not just one individual mineral, while quartz is one specific mineral that has many variations.

Additionally, the main element present in feldspar is aluminum, while the main element found in quartz is silicon.

While these are the most important distinctions, feldspar and quartz also differ in formation, hardness, cleavage, appearance, and gemstone classification.

Formation

As we’ve already established, feldspar is a group of minerals that form individually, but are so incredibly similar that they get lumped together.

All variations of quartz form the same way, but elements like temperature and what other chemical compounds are present during formation create numerous variations.

Compounds get trapped in the crystal structure while it’s forming, which causes the differences we see in quartz variations.

Hardness

The Mohs hardness scale is one of the best ways to determine the differences between minerals.

If two minerals are struck against one another, the harder of the two will scratch the softer.

Quartz ranks number 7 on the Mohs hardness scale, while orthoclase, a type of feldspar, rates at number 6.

This means that quartz is the harder of the two, and if the two were to be struck against each other, quartz would be unscathed while feldspar would be scratched.

This is a great way to tell the difference if you have two samples and are unsure which is which.

Cleavage

When minerals form, they always form in the same specific shape, which is called their crystal structure.

And when a mineral is smashed, it will either break into random, unpredictable pieces, or it will break into pieces of the same size and shape.

This is referred to as their cleavage.

Feldspar and quartz have different crystal structures, and therefore, different cleavages.

Feldspar has two perfect cleavages which meet at a 90-degree angle, which means that when feldspar is hit with a geologist’s hammer, the pieces will always look the same.

In contrast, quartz has indiscernible cleavage.

When quartz is hit with a geologist’s hammer, the pieces will all be random and break into different sizes and shapes.

Appearance

Relying on appearance will get any rockhound into trouble.

Like quartz, many minerals have all types of variations that depend on the conditions under which they form.

Quartz is usually colorless, but it comes in all types of colors.

Feldspar is typically white, but it, too, can be found in many different colors.

Therefore, there is a lot of overlap between these two minerals.

One main visual distinction is that feldspar is usually much cloudier than quartz.

When held up to the light, feldspar will look cloudy and the light will not shine through so clearly, while quartz will be clear and allow light to pass through more easily.

Still, it is best not to rely on appearance to tell the difference between any two kinds of minerals.

Gemstone Classification

Any mineral can be considered a gemstone if it has a pattern or color that people deem attractive.

Therefore, both feldspar and quartz have variations that are considered gemstones.

The difference is, that out of more than 200 recognized gemstones, at least 12 of those are variations of quartz, while only 4 of them are variations of feldspar.

This is most likely due to the fact that quartz is a harder mineral than feldspar.

If something can be scratched or broken more easily, it is considered less valuable.

Conclusion

While many people confuse feldspar and quartz because they are found in similar rocks and have similar chemical compounds, a quick read and a bit of research shows how different the two minerals really are.

Feldspar and quartz are two of the most commonly occurring minerals on this planet, so it really pays to be able to tell the difference!

Keep these facts in mind and you’ll have no trouble discerning feldspar from quartz.

Happy Rockhounding!