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

Rhyolite is an extrusive igneous rock and is high in silica content. This fine grained igneous rock will typically contain the minerals quartz, plagioclase, and sanidine with lesser amounts of biotite and hornblende.  Rhyolite is formed closer to the surface of the earth.

Both rhyolite and granite can be quite similar in appearance, however granite will form below the earth’s surface cooling slowly.  At times, many may see outcroppings of rhyolite and mistake the rock as granite.

With the high content of silica and lower content of elements such as iron and magnesium, rhyolite magmas will be highly viscous, or very thick and sticky consistency between being a solid and a liquid. 

Rhyolite is considered a aphanitic extrusive igneous rock. Aphanitic means that rhyolite contains crystals that are too small to see.

Rhyolite that cools very quickly will not produce large crystals but will form a natural smooth look.  Some rhyolite can take much longer to cool, this can form larger crystals.

Rhyolite Uses

The uses of rhyolite seem to be few.  In some cases rhyolite can be used as landscaping rocks, or crushed rocks, and can at times be sculpted into decorative rocks.  In the past, rhyolite was used as tools or weapons primarily due to its convenience and availability.

With the inclusion of some beautiful minerals that can be found with rhyolite, you can often find specimens of those minerals still attached to the rhyolite as they are displayed.

What is the Color of Rhyolite?

The color of rhyolite is typically a gray, tan, or pink.  There can be variations in the hue of these colors depending on the amount of different types of elements available.  Typically the colors of rhyolite are not too spectacular but the patterns that can be expressed can capture your attention.

Some rhyolite rock can express foliation, or banding, while others look almost sedimentary with larger looking inclusions in the rock.  With that, the inclusions in the rock are what can make this rock more exciting to look at.   

As mentioned, gem type minerals can often be found within some rhyolites. The contrast with the minerals and the rhyolite usually make a great combination for displayed specimens.  

What is Rhyolite worth?

The worth of rhyolite is small do to abundance and non-use. If purchasing less colorful looking rhyolite, expect to pay around $2 to $10 per pound. The worth of more colorful rhyolite such as wonderstone may valued well over $10 per pound.

Rhyolite is not really sold much unless one is obtaining a specimen at a rock and mineral show or rock and mineral shop. Keep in mind the larger the specimen the more costly it can get.

Rhyolite a Gemstone Bearing Material 

Rhyolite can contain gemstones and is considered a gemstone bearing rock. As the granitic lava cooled quickly, small “vugs”, or pockets of gas, were trapped within.  As hydrothermal gases and water moved through the rock, those pockets would precipitate with the surrounding elements over time to create gemstones.

Did you know that high silica content rocks, much like rhyolite, and a little bit of water can assist in the creation of opal? These deposits of hydrated silica find their way into cracks and pockets of host rocks to create some of the opal we see today.

For more information on opal and some pictures, you read my article “All About Opal“.

Some of those crystals found in rhyolite can be quartz type crystals such as amethyst.  In some locations there can be the presence of other elements such as aluminum which will form topaz.  In rare cases like red beryl, rhyolite will contain beryllium with aluminum and trace amounts of manganese to give it the red color.

Agate and jasper, also considered to be gemstones, will often be created in this similar manner within the pockets of host rocks.

For a closer look at some of these minerals that can be within rhyolite, I have written some great articles with more information and pictures for reference.

“All About Amethyst” – This is a very popular type of quartz.

“All About Topaz” – One of the more popular gemstones for jewelry.

“All About Red Beryl” – This gemstone is one of the rarest and most expensive in the world.

“All About Agate” – A very popular mineral amongst rock and mineral collectors due to colorful patterns.

What is Rhyolite Porphyry?

When people refer to rhyolite with the word porphyry, they are talking about the texture of the igneous rock. Rhyolite porphyry rocks can have a variety of different textures but usually the silica base part of the rock is finer grained than the larger grain inclusions of feldspar or quartz.

Rhyolite is too dense and does not float even though it is granular, fine grained, and can be somewhat porous. This also makes rhyolite difficult to take a polish, so attempts to do that may prove unfruitful.    

Rhyolite Contents

Rhyolite is made up of a silica rich content typically greater than 69%.  On the elemental level, along with silica and oxygen, rhyolite can have the additional content elements of iron, aluminum, manganese, sodium, potassium, and calcium along with others.

These elemental contents in rhyolite are available for those chemical reactions which create many minerals. Minerals such as quartz, feldspar, plagioclase, sanidine, biotite, and hornblende as mentioned above.  If the cooling process of lava is quicker, then expect rhyolite to be glassier and produce pumice, obsidian, perlite, and pitchstone.

Some eruptions of rhyolite can be highly explosive and those deposits may consist of tuff and ignimbrites.

Where can Rhyolite be found?

Rhyolite is a volcanic rock and can be found around previous volcanic activity where granitic magma made its way to the surface.  Rhyolite can be found all around the world with varying colors and textures but typically it will not be found in oceanic volcanic occurrences.