Chalcedony is a microcrystalline form of quartz, belonging to the silica-based stones. It is known for its dense structure, waxy luster, and the fact that many familiar gemstones are actually variations of chalcedony.

In this article, we will explore the properties, hardness, composition, and formation of chalcedony, as well as how stones like agate, onyx, carnelian, sardonyx, and blue lace agate relate to chalcedony.

💎 Interested in chalcedony? Explore all chalcedonies and chalcedony jewelry. See selection →

What is chalcedony?

Chalcedony is a microcrystalline or cryptocrystalline form of quartz. This means it is composed of very small quartz crystals that are usually not visible to the naked eye.

Unlike, for example, rock crystal, which grows as distinct crystal points, chalcedony forms dense, fine-grained masses. This often makes it appear smooth, slightly translucent, and with a waxy luster.

If you wish to read more about the symbolic aspect of chalcedony, please also see the article on the meaning of chalcedony.

You can also explore the structure and formation of other popular stones in the articles on amethyst properties, rose quartz properties, rock crystal properties, obsidian properties, labradorite properties, tiger's eye properties and moonstone properties.

Composition of chalcedony

Chalcedony is mainly composed of silicon dioxide, the same basic chemical substance as quartz. However, its structure is much finer-grained than that of quartz forming visible crystals.

Chalcedony may also contain small amounts of moganite, another mineral form of silicon dioxide. This is one reason why chalcedony is not always simply "small quartz", even though it belongs to the quartz group.

• belongs to the quartz group
• composed mainly of silicon dioxide
• is a microcrystalline or cryptocrystalline form of quartz
• may contain small amounts of moganite

Hardness of chalcedony

The hardness of chalcedony is generally about 6.5–7 on the Mohs scale of hardness. It is therefore very close to other stones in the quartz group, such as amethyst, rose quartz, and rock crystal.

Due to its good hardness and dense structure, chalcedony is well-suited for jewelry, tumbled stones, carvings, and decorative objects.

How does chalcedony form?

Chalcedony typically forms when silica-rich fluid or solution fills cavities, cracks, or pores in a rock. Over time, the silica precipitates into these spaces as very fine-grained quartz.

This process can produce uniformly colored chalcedony, layered agate, or other variations of chalcedony. The appearance of the stone depends on, among other things, the minerals, impurities, formation environment, and how the silica has been deposited.

Unlike, for example, obsidian, which forms from rapidly cooling lava, chalcedony forms gradually through the action of silica-rich fluids.

Color and appearance of chalcedony

Chalcedony can be white, gray, bluish, brown, orange, red, green, or almost black. The color is influenced by small amounts of other minerals and elements contained in the stone.

Many varieties of chalcedony are known precisely by their color or patterning. For example, carnelian is an orange-red chalcedony, while blue lace agate is known for its light blue and lacy bands.

Agate – layered chalcedony

Agate is a layered variety of chalcedony. It is known for its banded, striped, or otherwise patterned structures.

Agate occurs in many different colors and forms. Its patterning is created as silica gradually deposits into cavities or cracks within the rock.

Also explore blue lace agate, which is one of the best-known light blue agate varieties.

Onyx – a dark and striped variety of chalcedony

Onyx is a variety of chalcedony, particularly known for its layered structure. Mineralogically, onyx usually refers to banded chalcedony, where the layers can be, for example, black and white.

In the jewelry trade, the name onyx often refers to a uniformly black stone. Therefore, black onyx is familiar to many, especially from jewelry, beaded bracelets, and crystal practices related to protective themes.

Carnelian – orange-red chalcedony

Carnelian is an orange, reddish, or brownish-orange variety of chalcedony. Its warm color is linked to iron compounds that give the stone its recognizable hue.

In crystal practice, carnelian is often associated with courage, vitality, creativity, and the energy of action. Geologically, however, it is part of the same broad chalcedony group as agate and onyx.

Sardonyx – a layered sard and onyx type stone

Sardonyx is a layered variety of chalcedony that exhibits brown, reddish-brown, white, or dark bands. The name refers to sard and onyx, both of which belong to the chalcedony group.

Sardonyx has historically been popular for carvings and cameo jewelry because its layered structure is well-suited for bringing out patterns.

Bloodstone – a green variety of chalcedony

Bloodstone, also known as heliotrope, is a green variety of chalcedony. It is recognized by its green base color and red spots, which are usually caused by iron oxides.

Geologically, bloodstone belongs to the same chalcedony group as, for example, agate, carnelian, and onyx, although its appearance differs significantly from them.

Chalcedony in jewelry and everyday life

Chalcedony and its varieties are widely used in jewelry, beads, carvings, tumbled stones, and decorative objects. Its dense structure, beautiful colors, and good hardness make it a popular material for various stone products.

See Ametistikissa's chalcedonies

The significance of chalcedony for crystal enthusiasts

Among crystal enthusiasts, chalcedony is often associated with calm expression, balance, and gentle energy. However, its different varieties have their own symbolic meanings.

For example, onyx is often associated with protection and strength, carnelian with courage and vitality, and blue lace agate with peaceful communication.

Summary: key properties of chalcedony

• Chalcedony belongs to the quartz group.
• It is a microcrystalline or cryptocrystalline form of quartz.
• It is mainly composed of silicon dioxide.
• The hardness of chalcedony is generally about 6.5–7 on the Mohs scale.
• Agate, onyx, carnelian, sardonyx, and blue lace agate are related to the chalcedony group.
• Chalcedony is widely used in jewelry, carvings, and tumbled stones.

Frequently asked questions about chalcedony

Is chalcedony quartz?

Yes. Chalcedony is a microcrystalline or cryptocrystalline form of quartz, mainly composed of silicon dioxide.

What is the hardness of chalcedony?

The hardness of chalcedony is generally about 6.5–7 on the Mohs scale of hardness.

What stones belong to chalcedony?

Stones related to the chalcedony group include, for example, agate, onyx, carnelian, sardonyx, and blue lace agate.

Is onyx chalcedony?

Yes. Onyx is a variety of chalcedony. Mineralogically, onyx usually refers to banded chalcedony, but in the jewelry trade, the name often also refers to a uniformly black stone.

How does chalcedony form?

Chalcedony forms when a silica-rich fluid or solution fills cracks, pores, or cavities in a rock and precipitates into them as fine-grained quartz.