agate vs. chalcedony vs. jasper

Chalcedony, agate and jasper are all quartz based stones that encompass a large amount of crystals we know and love. If you have a crystal collection, you definitely have some of these crystals in your collection. Sometimes these terms can be used interchangeably, but each category has slight differences that differentiate them from each other. Since all of these crystals are all described as microcrystalline varieties of quartz, it can be hard to see what the difference between them is. There is a lot of mislabeling when it comes to these terms, so it’s important to understand the differences.

Chalcedony is the general name for microcrystalline varieties of quartz. Microcrystalline means the grains are so small you would need a microscope to see them. Jaspers and agates are both varieties of chalcedony, but the terms aren’t interchangeable. For example, blue chalcedony is a microcrystalline quartz that isn’t an agate or jasper. It is only a chalcedony. Whereas carnelian is an agate, therefore it is also a chalcedony. Chalcedony is semi-transparent to translucent. Translucent means that some light is let through the stone, but it isn't entirely clear like clear quartz. Carnelian is a great example of a translucent chalcedony; if you look at carnelian in the sunlight it has a bit of a glow to it because of the light shining through. 

Even though chalcedony is composed of quartz, there are some differences between chalcedony and just quartz. They both have conchoidal (no natural planes of separation) fractures, but quartz will have a glassy luster and chalcedony will have a dull luster due to its crystallization. 

 Examples of chalcedony: blue chalcedony, purple chalcedony, chrysoprase 

Grape "agate" is an example of a botryoidal purple chalcedony. Botryoidal means having a round crystal formation; grape agate is the perfect example of this. Not all botryoidal crystals are composed of chalcedony, many different minerals form this way. Prehnite and hematite being non-quartz minerals that can form botryoidally. 

Agate is a translucent to semi-transparent variety of microcrystalline quartz identified by its banding. Agates are very often dyed, or heated to enhance color. Carnelian is a variety of agate, and a lot of carnelian on the market is heated to enhance its red/ orange color. Natural carnelian tends to be more on the brown side without color enhancement. Dyed agates will often be seen in unnaturally bright shades of blue, purple or pink. These are usually found in tumble or slice form, and are extremely cheap and one of the most commonly dyed crystals. 

Flower agate and moss agate are examples of agates that may or may not have visible banding, but still fall within the agate category.

Carnelian agate with banding and moss agate inclusions

Onyx is another microcrystalline quartz that is very similar to agate. Onyx is characterized by parallel banding and if not dyed, onyx is usually found in black, white or shades of brown. Unfortunately, much of the black banded onyx on the market is dyed. Onyx is very often mistaken for banded calcite, as they both have this very straight banding. 

Sardonyx is a red variety of onyx, with alternating sard & onyx layers. Sard is a reddish brown variety of chalcedony which is often used interchangeably with carnelian. The only difference between them is their color, and there isn't a clear boundary of where it becomes carnelian instead of sard. Though by definition onyx has parallel banding, sardonyx has more of a crazy banding and doesn't look like typical onyx. 

It's hard to identify a stone as onyx vs. agate just by how straight the banding is. High quality blue lace agate can have very straight and parallel banding and is still classified as an agate. If not dyed, onyx is usually found in black, white or shades of brown. 

Sardonyx

Examples of agate: carnelian agate, Botswana agate, crazy lace agate, blue lace agate, moss agate, iris agate, flower agate 

Blue lace agate, orca agate, crazy lace agate, regular agate

Jaspers stand out from other microcrystalline quartzes because they are usually completely opaque. A more scientific name for jasper is chert or flint. Jaspers can sometimes be semi-translucent, but are most often opaque. They are typically seen in reds and browns, but can vary in color. Jaspers often have many impurities, therefore they are not one specific mineral but a rock. The word “jasper” is sometimes thrown around when it comes to trade names, which can lead to mislabeling and confusion. 

Examples of jasper: mookaite jasper, ocean jasper, polychrome jasper, red jasper, bloodstone jasper, yellow jasper, zebra jasper

Mookaite, ocean jasper, polychrome jasper, red jasper

The best way to determine the difference between agate and jasper is the amount of light that is let though the stone. Agates typically allow more light through, whereas jaspers are pretty opaque. It can be difficult sometimes to draw the line between these two, but if you're unsure, chalcedony is always a correct label for any type of microcrystalline quartz. 

Since all of these labels are extremely similar, it's easy for them to get mixed up and used incorrectly. Here are some examples I've seen of mislabeling within the crystal market. 

• Grape agate is not truly an agate; it fits better under the chalcedony category. The best name for this mineral is purple botryoidal chalcedony 
• “Dalmatian jasper” is not a jasper at all, but an igneous rock composed of feldspar and quartz
• Similarly, "kiwi jasper" is also not a jasper. It is composed of quartz, amazonite and tourmaline
• Bumblebee jasper is also not a jasper! Bumblebee “stone” is lithified volcanic sediments containing mostly calcite, and contains no quartz at all!