How is an Opal formed
by Steve Smith writer


https://www.apsense.com/article/how-is-an-opal-formed.html


Most of the gemstones that are found are treated artificially either by heating them at a certain temperature or by adding some kind of chemicals in them. But Opal is the only gemstone which does not undergo any type of artificial treatment.

After reading this article, you will have a very clear idea about the exact process on how an opal is formed

Opal, the natural gemstone forms in a very interesting way. It is formed from a combination of silicon dioxide and water. The stone is truly natural and is formed in a very beautiful manner. When water runs down through the earth, it collects all the silica present in the sandstone. This solution is formed by natural decomposition. When the water finally evaporates under extreme conditions of heat, then it forms small oval structures which take the shape of an opal when they are hardened.

The silica rich solution which is formed in the volcanic rocks creates cracks and voids by the weathering process. Many fossils releases molds that acts as a secondary mineral in the formation of this gemstone. Miners call it by the name of potch and the mineralogist terms it as Common Opal. During the initial formation, the gemstone is in its unnatural state and therefore many pores are formed in it. Opaline Silica fills all those pores, thereby accumulating all the grains.

Variation inside an opal depends upon a number of factors. Climate plays an important role in the formation in the variation. Wet climate helps to maintain the amount of silica inside the stone where as a dry climate significantly reduces the water content inside the stone thereby making it harder. Moreover, regions where volcanic eruptions take place also a material known as the white kaolin is formed and thereby it helps to produce an Australian Opal.

Many scientists as well as mineralogist are still researching in order to find out the exact way by which an opal is formed. They are constantly trying to figure out the chemical conditions or the acidic reactions that are responsible for the creation of an opal. Opals mainly have their origin from the Great Australian Basin. Three other places that are Lightning Ridge in New South Wales, South Australia and Queensland boulder where black white and matrix opals are found respectively.

Another important member in the family of Opal is the Boulder Opal. Even this gemstone is formed naturally. But the appearance of such kind of opals is quite different. These stones are generally elongated in shape. They are mainly formed by the accumulation of sandstones. Though, some minute cracks might develop in this opal but it does not affect the appearance of the stone in any way. Boulder opals are cut into fine precision by the gem cutters to give them the desired shape.

Matrix and Pipe are the two important opals that are yet other members of the opal family. Matrix Opal is very rare in existence and they are mainly formed by iron stone. Pipe Opal on the other hand is like a pipe structure that is usually longer in shape. Hence, Opal Beads are one of the most natural gemstones that are found on earth.

you left out super man

oh wait
that was for diamonds

never mind

Thanks for that interesting article. It is written in language that is easy to understand.

Your welcome.

I like Opals and in discovering how they are formed make them even more interesting.

Here is a list of minerals as well

http://geology.com/minerals/

Andalusite
Anhydrite
Apatite
Arsenopyrite
Augite
Azurite

Barite
Bauxite
Benitoite
Beryl
Biotite
Bornite Calcite
Cassiterite
Chalcocite
Chalcopyrite
Chlorite
Chromite
Chrysoberyl
Cinnabar
Clinozoisite
Copper
Cordierite
Corundum
Cuprite Diamond
Diopside
Dolomite

Enstatite
Epidote

Fluorite
Fuchsite

Galena
Garnet
Glauconite
Gold
Graphite
Gypsum Halite
Hematite
Hornblende

Ilmenite

Jadeite

Kyanite

Limonite Magnesite
Magnetite
Malachite
Marcasite
Molybdenite
Monazite
Muscovite

Nepheline
Nephrite

Olivine
Orthoclase Plagioclase
Prehnite
Pyrite
Pyrophyllite
Pyrrhotite

Quartz

Rhodochrosite
Rhodonite
Rutile Scapolite
Serpentine
Siderite
Sillimanite
Silver
Sodalite
Sphalerite
Spinel
Spodumene
Staurolite
Sulfur
Sylvite Talc
Titanite
Topaz
Tourmaline
Turquoise

Uraninite

Witherite
Wollastonite

Zircon
Zoisite

What is a Fluorescent Mineral?

http://geology.com/articles/fluorescent-minerals/

All minerals have the ability to reflect light. That is what makes them visible to the human eye. Some minerals have an interesting physical property known as "fluorescence". These minerals have the ability to temporarily absorb a small amount of light and an instant later release a small amount of light of a different wavelength. This change in wavelength causes a temporary color change of the mineral in the eye of a human observer.

The color change of fluorescent minerals is most spectacular when they are illuminated in darkness by ultraviolet light (which is not visible to humans) and they release visible light. The photograph above is an example of this phenomenon.


Fluorescence in More Detail

Fluorescence in minerals occurs when a specimen is illuminated with specific wavelengths of light. Ultraviolet (UV) light, x-rays and cathode rays are the typical types of light that trigger fluorescence. These types of light have the ability to excite susceptible electrons within the atomic structure of the mineral. These excited electrons temporarily jump up to a higher orbital within the mineral's atomic structure. When those electrons fall back down to their original orbital a small amount of energy is released in the form of light. This release of light is known as fluorescence. [1]

The wavelength of light released from a fluorescent mineral is often distinctly different from the wavelength of the incident light. This produces a visible change in the color of the mineral. This "glow" continues as long as the mineral is illuminated with light of the proper wavelength.

the fluorescence phenomenon
Diagram that shows how photons and electrons interact to produce the fluorescence phenomenon.


How Many Minerals Fluoresce in UV Light?

Most minerals do not have a noticeable fluorescence. Only about 15% of minerals have a fluorescence that is visible to people and some specimens of those minerals will not fluoresce. [2] Fluorescence usually occurs when specific impurities known as "activators" are present within the mineral. These activators are typically cations of metals such as: tungsten, molybdenum, lead, boron, titanium, manganese, uranium and chromium. Rare earth elements such as europium, terbium, dysprosium, and yttrium are also known to contribute to the fluorescence phenomenon. Fluorescence can also be caused by crystal structural defects or organic impurities.

In addition to "activator" impurities, some impurities have a dampening effect on fluorescence. If iron or copper are present as impurities they can reduce or eliminate fluorescence. Furthermore, if the activator mineral is present in large amounts, that can reduce the fluorescence effect.

Most minerals fluoresce a single color. Other minerals have multiple colors of fluorescence. Calcite has been known to fluoresce red, blue, white, pink, green and orange. Some minerals are known to exhibit multiple colors of fluorescence in a single specimen. These can be banded minerals that exhibit several stages of growth from parent solutions with changing compositions. Many minerals fluoresce one color under short-wave UV light and another color under long-wave UV light.


Fluorite: The Original "Fluorescent Mineral"

One of the first people to observe fluorescence in minerals was George Gabriel Stokes in 1852. He noted the ability of fluorite to produce a blue glow when illuminated with invisible light "beyond the violet end of the spectrum". He called this phenomenon "fluorescence" after the mineral fluorite. The name has gained wide acceptance in mineralogy, gemology, biology, optics, commercial lighting and many other fields.

Many specimens of fluorite have a strong enough fluorescence that the observer can take them outside, hold them in sunlight then move them into shade and see a color change. Only a few minerals have this level of fluorescence. Fluorite typically glows a blue-violet color under short-wave and long-wave light. Some specimens are known to glow a cream or white color. Many specimens do not fluoresce. Fluorescence in fluorite is thought to be caused by the presence of yttrium, europium, samarium [3] or organic material as activators.

You seem to like rocks and minerals, are you a prospector at heart?

Interesting Posts!

lol, possibly. I am always wondering how things are made or why something works I ask questions on a lot of subjects. Would I go out looking for rocks and minerals? Maybe once just to see what I could find.

There is a lot of info on rocks and minerals . A few books are worth the read as well.

There's gold in them thar hills! Might have to go out more than once to find the motherlode. I have been looking for years.

You are obviously looking in the wrong place.Try Mingle you might find some nuggets there.

Nuggets or gold diggers from Nigeria?

How long have you been looking for gold ?

I worked for exploration companies off and on since I was a teenager, so have been prospecting as a hobby ever since. Wanna see my rock collection?

In that case it might be better to hold on to your nuggets

I think it's a good idea to hang onto your nuggets all the time!

Depends on who's volunteering to hold them.

The princess who was holding mine turned into a dragon. I was lucky to get them back.