Agate and Geode are beautiful rock pieces that both rock collectors and spiritualists value. The former is a banded variety of chalcedony while the latter are spherical rock structures that have an internal cavity of minerals.

Have you ever wondered how agate and geode differ from each other? In this article, we are going to discuss just that. We will begin by introducing the two minerals. Then we will talk about their similarities and differences. Finally, we will learn about distinguishing one from the other. 

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What is Agate?

Agate is a banded variety of chalcedony, which is a cryptocrystalline form of quartz. Its use in jewelry goes as far back as the 3rd millennium BC when it was used for bead necklaces in the Indus Valley Civilisation.

Agate got its name from the Greek philosopher Theophrastus, who found the stone along the shoreline of the Dirillo River or Achates. In Ancient Greece, agate was commonly used as an ornament in assorted jewelry and the seal stones of Greek warriors.

Existing in a wide variety of vivid colors, agate is distinguished by its beautiful bands that create unique swirls & marks on the rock. The coloration comes from impurities in the chalcedony base (oxides of iron, manganese, titanium, etc.) while plumes & moss-like patterns are the result of other minerals trapped inside the silica during formation.

Designers usually take advantage of these naturally-occurring patterns to create fascinating pieces. Moreover, agate takes an excellent polish and is hard enough for most jewelry uses. All of this makes it a significant jewelry stone. 

Agate is primarily formed in nodules but can also occur in large veins and seams of differing rock layers. It is often formed in the cavities of volcanic rocks during the cooling of lava or magma. After the rock has solidified, water (carrying minerals) seeps into it and creates layers within it.

Like other cryptocrystalline quartz varieties, agate has a conchoidal fracture. Agate has a value of 6.5 to 7 on the Mohs Hardness Scale, so it is quite hard; this makes it rather difficult to work with by hand, and even with the right tools, it can sometimes be exhausting. 

What is Geode?

Geodes are hollow, somewhat spherical rocks that contain masses of mineral matter inside them. They are not exactly a specific kind of stone but more of a general description of many stones. 

These can form in any cavity, but the term “geode” is usually reserved for spherical-shaped formations occurring in igneous and sedimentary rocks. In igneous rocks, they can form in gas bubbles (such as vesicles in basaltic lava), and in sedimentary rocks, they occur in rounded cavities.

The rock around the cavity hardens and then dissolved silicates and/or carbonates seep inside the rock. Eventually, this slow movement of mineral constituents from groundwater or hydrothermal solutions creates crystals inside the hollow stone.

Finally, the bedrock containing Geodes weathers and decomposes, leaving only the geodes (since they are made of more resistant material, that is, quartz). Geodes can be as small as a coin or extremely large (such as the cathedrals of amethyst found in Brazil). The main sources of commercial geodes are Brazil, Uruguay, and Namibia.

Geodes get their coloration and banding due to impurities. Iron oxides will impart a reddish hue to siliceous solutions, such as iron-stained quartz. Geodes can contain various crystals: quartz, amethyst, chalcedony, etc.

Similarities Between Agate and Geode

The similarities between agate and geode are:

• Formation: Agate and geode are both formed similarly. They develop in cavities within rocks. Groundwater or hydrothermal solutions containing minerals seep into these rocks, which then get crystallized. Both agate and geode usually form in igneous rocks.

• Range of colors: Both agate and geodes come in a wide variety of beautiful colors: blue, red, green, etc. They also show unique patterns of bands or moss-like structures, which are the result of impurities.
  
• Minerals: Chalcedony is a key mineral for both agate and geode. Agate, as we saw, is a banded variety of chalcedony, so the whole structure is made out of it. The mineral also forms on the walls of the stone in Geodes, allowing other crystals to grow.
  
• Hardness: Both geode and agate are quite hard. Agate has a value of 6.5 to 7 on the Mohs Hardness Scale while geode’s value is between 6.5 to 7.5. This means that both are reasonably hard minerals, which is why they are widely used in jewelry. 

• Abundance: Both agate and geode are common specimens; they can be found in many places across the planet. Banded agate mainly comes from Mexico, Brazil, and USA. Geode, on the other hand, is primarily obtained from Brazil, Uruguay, and Namibia.

Differences Between Agate and Geode

These are the differences between geodes and agates:

• Specificity: The terms “geode” and “agate” differ in terms of their specificity. Agate is a specific type of mineral: a variety of chalcedony that has bands due to impurities. Geode, on the other hand, is more of a general description of hollow stones containing minerals inside them. So, it can refer to a range of stones, containing different minerals.

• Crystal size: Agate and geodes have different crystal sizes. Agate is a type of chalcedony, which is a cryptocrystalline quartz. This means that its crystals are quite small and they cannot be seen without magnification. Geode, on the other hand, has macro crystals. So, you can see them with your naked eye.
  
• Structure: The two are quite different in terms of their structure. Agate is made up of chalcedony, and this mineral creates a fully-occupied solid structure. Geode, on the other hand, is hollow. It only contains linings of minerals inside it.
  
• Appearance: Agate and geodes are quite different in their appearance. Agates usually have symmetrical bands and markings on their surface. In contrast, geodes have a more irregular appearance, with a range of crystals forming unique patterns. Agates are known for their colorful bands, which are due to impurities of other minerals. Geodes also have inclusions, but they are not as common as in Agates.

• Weight: Agates are usually heavier while geodes tend to be lighter. Their weight is often a good way of identifying them in the field: simply hold an unbroken stone in your hand and judge whether it’s agate or geode. 

• Sources: Although both agate and geodes are commonly found, they come from different types of rocks. Agates are usually found in volcanic or sedimentary rocks while geodes are usually found in limestones.
  
• Astrological & Spiritual Beliefs: Agate and geodes are associated with different spiritual beliefs. Agates are associated with Gemini and Virgo Zodiac signs, and the stone is said to be linked to the Moon. Geode, on the other hand, is associated with a wide range of Zodiac signs, depending on its composition. So, a Celestite Geode would be linked with planets Neptune & Venus; it would also be associated with Gemini, Libra, and Taurus. 

Read: 13 Different Types of Purple Rocks and Minerals (+Pics)

Besides their zodiac associations, the two stones are also believed to have different spiritual properties. Agates are said to be cleansing stones that harmonize and rebalance emotions. They bring safety & security by removing negative energies. Agates are also believed to be connected with the Third Eye & Crow; they bring spiritual awareness & enlightenment.

Geodes, in contrast, can have a range of effects, depending on the minerals present inside them. For example, Citrine Geode is believed to bring confidence and energy. Again, the chakra also depends on the crystals. Amethyst Geode is associated with the Third Eye, while Clear Quartz Geode is linked to the Crown. 

How To Identify Agate From Geode?

There are several differences between agates and geodes. To identify them, you can use these differences (such as weight, appearance).

Since geodes are hollow, they usually tend to be lighter than other stones. Agate, on the other hand, is relatively heavier. So, pick up an unbroken stone, and feel its weight in your hand: if it’s lighter, then it’s probably a geode.

A much more precise way of identifying them is by opening the rock and checking their internal appearance. Agates will be solid, with some small voids (called vugs) that are lined with small quartz crystals. Geodes, on the other hand, are hollow, and there would be mineral crystals growing toward the center.

At times, distinguishing between the two can be quite difficult. This is especially true when you are dealing with Thundereggs. These are similar to Geodes and are often named as such. However, they are a unique variety of agate, which is filled with chalcedony and other minerals like opal. They usually occur within rhyolitic volcanic ash layers and are as big as a tennis ball.

Read: Garnet vs Ruby (Properties & Composition)

Conclusion

In this article, we have looked at agate and geode. Both are common rocks that are formed via similar processes, come in a range of beautiful colors, and are hard enough for jewelry purposes. However, they also have many differences, the most significant among which is their specificity: agates are a specific kind of chalcedony while geodes are more of a general description for a wide range of stones.