How are opals formed?

How are opals formed?

Opals are among the most enchanting and unique gemstones in the world, although this may be a personal view. In fact, opals are known for their fascinating colour games. They can display beautiful and incredibly deep colours, from blues and greens to a pure orange and red.

These colour appearances make opals a favourite among collectors like myself, as well as jewellery makers. But how is an opalactually formed? Let's take a closer look at that together.

What are opals?

Let's first talk about what an opal actually is before discussing how they are formed. Opals are hydrated silica, meaning they consist mainly of water and silica (SiO2). This mineral can occur in amorphous but also crystalline form. For opals, the amorphous form where molecules are not arranged in an ordered pattern is important. Indeed, this structure is responsible for the opal's unique light and colour spectacles.

How opals are really formed

The formation of opalsis a process that occurs only under very specific conditions. The process starts when silica-rich water travels through the Earth's crust and enters cracks or between layers of rock. This can happen in different environments, for example: sedimentary rocks and around hot springs.

Step 1: solution and transport

Rainwater absorbs silica from the earth and rocks, creating a kind of gel-like mix. This water then eventually moves through cracks and holes in the ground.

Step 2: gel formation

Once the process and gel are perfunctory, such as when the water starts to evaporate or when something changes with the acidity, silica starts to leak from the mix and forms a kind of thick, gel-like substance. This is ultimately the base of the opal.

Step 3: hardening

This can often take a long time, often millions of years in most cases. The gel or base of the opal slowly loses its water and hardens into an opal. Because this process can vary in speed and, more importantly, conditions, we see diversity in the opal group as we know it today.

Opal species

There are an awful lot of different types of opals There are different types of opals, each with its unique characteristics and formation process. The most well-known types are:

Precious opals

Precious opals are known for their brilliant colours, which are created by light reflecting off incredibly small silica spheres that the opal is made up of. These spheres are all the same size and neatly arranged in a row, creating the beautiful rainbow colours.

Fire piles

Fire opals are in most cases transparent to translucent. The opals vary between the colours yellow, orange and red. These opals contain less water than the precious opal and are most commonly found or perhaps only found in volcanic areas.

Common opals

Plain opals, have little to no diversity of colours and are often white, grey, brown or black. These opals are mostly used as background filler in opal jewellery to enhance the colours of noble opals.

What role does water play?

Water plays an incredibly important role in the formation of opals. Not only is it the main player in transporting the silica, it also helps gel formation afterwards. The amount of water in an opal can range from 3% to 21%, which contributes incredibly to the unique properties of each stone. The water content affects not only the opal's hardness and stability, but also its colours. The higher the percentage of water is, the more likely the opal is to display incredibly vibrant colours. The downside of this is that the stone is also much more susceptible to drying out and cracking.

How do I keep my opals looking good?

It is incredibly important to take good care of your opals. This is because opals need to be well protected from extreme temperatures or temperature fluctuations but also from environments that can lead to dehydration. When you choose to wear opals, the opal can be supplied with moisture by the natural moisture of the skin. In addition, you don't want to introduce your opals to harsh chemicals or cleaning products either. These can affect your opals very negatively.


We at Megalodontand.nllove good research on opals which we in turn can share with you. Well, I must say that this may have been a very extensive research, however, I like to share the passion when it comes to gemstones and minerals with everyone.

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