Agate vs. Opal: Is There a Difference?

Agate and opals both are both beautiful gemstones to look at, each offering very unique patterns and colors.  While there are some similarities, there are a lot of differences that should be known.  In today’s post, let’s discuss the differences between agate and opal gemstones.

What is agate?

Agate is a type of quartz that is characterized by banded patterns.  It’s made of a banded microcrystalline Quartz, which is one of the two elements found inside chalcedony.  This quartz is so small that it can only be viewed under a microscope.  These crystals are formed when the silica-rich fluids from previous volcanic activity fill between layers of a rock, slowly hardening into quartz over time.  We’re talking hundreds of thousands of years.  It is this banding that you see that is the key difference in the composition of the silica as it solidifies over the years.

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Agate comes in many colors, almost any you can think of, such as blue, green, red, black, white, black and many more.  These colors, in comparison to opals, are a softer color, not so vibrant, in comparison to an opal.  Opals are more known for their vibrant color.  The banding you see on an agate will vary with so many unique pieces available.  Some banding will be thin and closely spaced, whereas some agates have sweeping bands, almost like a wave swept through.

Agates are found all around the world; however, it’s most commonly associated with Brazil, Mexico and the United States.  You can find agates in volcanic rock, sedimentary rocks and metamorphic rocks, often in the cavities of a rock or even in a river bed, where the water has smoothed out the surface over time.

Throughout history, agate has been known for both its beauty as well as the healing properties it was said to give.  Many years ago, agates were believed to have magical powers that were able to protect those from danger.  These agate stones were then turned into beautiful pieces of jewelry as well as decorative objects.  While it’s still popular today, many use agates moreso for jewelry and decorative purposes.

What is opal?

Opal is a hydrated amorphous silica, and this simply means it doesn’t have a crystalline structure.  Similar to that of agate, it forms when a silica-rich fluid seeps into a crack of a rock, and as time progresses, the fluid will then solidify into a gel-like substance.  As this gel dries, it will then form these tiny spheres of silica, which will then stack to create a random pattern.  It’s the spaces that you see between these smaller spheres that can create that opal light scattering effect as well as various random patterns.

Opals, like agates, have a range of colors, mainly white, black, red, orange, yellow and blue, to name a few; however, your more valuable opals will be the brighter, more vibrant colors with a high degree “play of color.” Unlike agates, which have a softer look, an opal will have a shimmering, rainbow-like appearance, which is created when light diffracts as it passes through the gemstone.

Opals are commonly found in Australia, Brazil, Mexico and the United States.  Like agates, you can find them in sedimentary rocks, metamorphic rocks as well as volcanic rocks.  Most miners will find opal in dryer, desert-like regions, as this is where the silica-rich fluids seeped into the cracks.

For centuries, opals, like agates, were believed to have magical powers, too.  People believed that opals brought good luck to whoever wore them.  This is still the thought today, but some simply wear opal jewelry as a fashion statement.

Agate vs. Opal

There are several differences between these two stones, but one major difference is how they were formed.  As mentioned, opals are formed when the silica-rich fluids seep into the cracks, whereas agates are formed when this silica-rich fluid fills the space between the layer.

Similar to that of formation, the crystalline structure is a key difference as well.  Opals are a type of hydrated amorphous silica, and this simply means they don’t have a specific crystalline structure.  However, agates are a type of quartz and will have a crystalline structure.

Another difference is how they look.  Agates come in almost every color imaginable as well as banded patterns.  After all, it’s the banded patterns that distinguish agate from other types of chalcedony and stones.  Opals are more known for their vibrant “opalescence” unique colors and patterns; however, you will never find a banded pattern.  While an opal can come in a range of colors, the colors are much more vibrant with a higher degree of color.   Agate colors are softer.

If we’re talking about birthstones, opal is the official birthstone of October, whereas agate doesn’t have a traditional month.

Lastly, the value and rarity is another key difference.  Since opals are much rarer than agate, you will find that opal will always cost much more than that of an agate piece.

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About Me

Hi! I'm Lauren, and I run Moonlight Gems AZ. I'm an avid crystal collector and would love to share my expertise with you.