Melinite opal

In this article, we’re going to explain what melinite opal is. Let’s go!

Quartz on Our Planet

Quartz is one of the most common minerals on Earth’s outer layer, found in pretty much all kinds of rocks. If you look at it by itself, it’s the most common mineral. However, if you group all the feldspar minerals together, there are more of them than quartz.

But quartz isn’t just common; it also comes in many different types. You might have heard of some of them, like amethyst (purple), rose quartz (pink), citrine (yellow), or agate (banded).

People use quartz for lots of things, like making filters, in things like ceramics and glass, and even in digital and precise devices because of a special property it has. Also, some types like amethyst and tiger’s eye are used as pretty gems in jewelry.

Opal

Another type of quartz is opal, and it’s very special in the jewelry world because of how pure it can be and how it shines light. People used to think opal was a mineral because it’s often found with another mineral called chalcedony. But if we’re being super strict about what a mineral is, opal isn’t quite one. That’s because it’s made of a glassy type of silica and doesn’t have the organized crystal structure that real minerals need.

Opal usually shows up in different kinds of rocks formed by hot water processes. In sedimentary rocks (rocks formed from bits of other rocks), it appears through other processes and can even help fossils form. Sometimes, you can find opal that has fossils of plants inside (called wood opal) or the shells of tiny sea creatures that had silica in them.

Opal is the only gemstone we know that can bend light and split it into all the colors of the rainbow! This is why it’s always been a very loved gem. Besides its shine, opal also comes in many colors like gray, white, brown, purple, yellow, orange, green, or even clear. Pure opal is usually clear or milky, but other minerals can give it different colors, like iron oxides that can make it look yellowish-brown. But mostly, the color you see in opal is from how light bounces off the layers inside, creating a shimmering, pearly look.

Melinite Opal

Now, let’s talk about a kind of opal that’s a bit unusual and not very well-known: melinite opal. These are whitish stones with interesting, round or flat shapes. They’re formed when silica material settles around gravel and sand. You often find them with diatomites or diatomaceous earth. Diatomaceous earth is a soft, crumbly rock made from the tiny fossils of diatoms, which are single-celled algae with skeletons made of silica. You usually find this material in shallow sea or lake sediments that are from a time long ago called the late Miocene.

Melinite opal is usually made of a core of opal that’s covered by diatomaceous earth. If you take off that outer layer, you’re left with the opal, which looks a bit like flint, a close “cousin” of opal.

These interesting shapes often turn up in places where old human settlements were found. One common shape is several little balls joined together, which can sometimes look a bit like a tiny human figure. Because of this, people have called them “little idols” and think they might have been symbolic objects in Bronze Age settlements in southeastern Spain. We don’t know for sure if they were tools or had a special, mysterious purpose. But some studies suggest that they might have been used as game pieces during the Iberian and Roman times.

In southeastern Spain, specifically in a place called Agramón, they’ve been called “bolas de camaretas” (which means “firecracker balls”). Near a place called the Camarillas reservoir, there are large areas of diatomites mixed with another material where you can find thousands of these unusual stones. In some of them, you can even find fossils of tiny shellfish, like Turritellas, as you can see in the pictures.