Sodalite is a stone that has shocked people in the past with the revelation that it can glow! And with this illuminating news (pun intended), I seen some people ask about whether sodalite is radioactive. So what’s the deal? The fact is, sodalite is not radioactive. It is sometimes mistaken as much due to its tendency to glow brightly in UV light or in the dark – however, that is not due to radioactivity. It is in fact due to the way it reacts to UV light.
Is Sodalite Radioactive?
Radioactive stones or rocks will typically contain uranium, potassium or thorium. Sodalite does not possess any of these elements in its natural composition. While radioactive rocks and gemstones are often formed within the earth’s crust under high pressure, as is sodalite, the compositions of the two types of rocks or gemstones are as different as can be.
Sodalite is a rare mineral that occurs in igneous rocks crystallized from sodium rich magmas. The crystal has been called “a salty combination of manganese and calcium” – leading geologists to propose that the name may have been partly derived from Sodium.
Sodalite can be blue, gray, yellow, orange or pink while in rock form. Gemstone quality sodalite ranges in color from violet to royal blue, with creamy veins and flecks. Large chunks of sodalite rock are opaque, but gem quality crystals can be polished to a high gloss and elegance, to the point of translucence.
The reason sodalite has gained some reputation as a radioactive gemstone is its ability to glow in the dark or in ultraviolet light – a phenomenon also common in rocks that are actually radioactive. But the reasons are different as we articulate below.
Can Sodalite Glow?
Sodalite definitely glows, both in its natural state and when polished. It is a fluorescent mineral. Let’s see some specific examples.
Though the Western world first “discovered” sodalite in the early 19th century, and then it gained popularity when veins of the rock were discovered in Canada towards the very end of that same century, the translucence and beauty of sodalite has been known for thousands of years to the ancients – this is why sodalite (along with its cousin, Lapis Lazuli) has been used as construction stones in sculptures and buildings all over ancient India, Egypt, Sumeria, Assiriya and China.
The blue colored stone has been known as a stone of peace, or the stone of truth, or the poet’s stone – based on ancients’ beliefs that it could connect with our powerful fifth chakra, the Visuddha or “Pure” chakra, located at the back of the throat towards the neck. The stone was thought to bring down negativity in emotions and thoughts, promote positive energy, cogent thought and superior powers of expression. But above all, there continues the feeling that these rocks glow in the dark.
One reason some varieties of sodalites stand out in the dark is that they develop underground, away from UV rays, and their colors fade in the sunlight. In other words, they glow in the dark – a phenomenon the lay person conflates with radioactivity. An example of such “glowing” is seen in Hackmanite, named after the Finnish geologist Victor Hackman.
Unlike other sodalites, hackmanite changes color significantly when exposed to sunlight. Pink or purple in its natural state, the mineral will fade to grayish or greenish white when exposed to sunlight. However, unlike crystals that lose color permanently, hackmanite will gain back its original purple color if kept away from sunlight. Some hackmanites may need to be kept in dark for a long time, up to a week, before regaining their natural color. This tenebrescence effect can be repeated indefinitely, unless the mineral is subjected to heat.
Another famous story came to light a couple of years back, when a gemstone dealer, Erik Rintamaki, discovered plain rocks on the beaches of Lake Superior that seemed to glow (bright amber and golden). The fluorescence was so pronounced that the photos and story went viral. The rocks emitted a particularly potent glow when exposed to UV radiation – the rocks seemed to be molten, as if lava. Rintamaki named the rocks “yooperlites”, after the locals who inhabit the Upper Michigan peninsula.
Why Does Sodalite Glow?
As it turns out, sodalite glows due to the fact that the mineral typically has streaks or veins containing compounds that produce the equivalence of luminescence or phosphorescence.
In terms of the rocks found in the Upper Michigan peninsula, they were examined in detail by a team from the University of Saskatchewan and Michigan Tech University, who subsequently published their findings in the Mineral News magazine. It turned out that the rocks contained large amounts of sodalite, a fluorescent mineral, but the effect was bolstered by the fact that the basic mineral composition was syenite.
This is an intrusive rock that forms within the magma layers below the surface of the earth, precipitated by the slow cooling of the hot magma. They contain pyroxenes and anphiboles, which make them darker than granite – but syenite crystals have a prominent quality that also leads to fluorescence, their crystals can expand to a few millimeters, and even centimeters, wide. So the rocks on the shores of Lake Superior had two types of minerals, both fluorescent, mixed in – augmenting the glowing effect.
The reason Hackmanite glows is different and actually a much rarer phenomenon occasionally found in nature. Hackmanite is a sulfur-rich variety of sodalite. This mineral possesses an extremely rare quality called tenebrescence or “reversible photochromatism”. The stone bleached by sunlight will revert back to its original pale or dark purple color when bought back indoors, similar to how photochromatic eyeglass lenses behave.
As you can see from the above analysis, sodalite does glow in the dark, but such a glow is most likely produced by specific minerals trapped within the veins of the rock – which can stand out prominently when polished to gemstone quality – as opposed to radioactivity.
The study by the two university teams concluded that while sodalite just appears blue-gray with white streaks when viewed with the naked eye, and none of its core elements (oxygen, sodium, silicon, chlorine and aluminum) are radioactive, something different happens when sodalite is placed under long-wave ultraviolet light. More precisely, the rocks light up, revealing the orange-yellow veins that produce an “incandescent” appearance. This is, of course, how fluorescence takes place – when stones are able to absorb longer wavelength rays and emit shorter wavelength ones themselves.
What Makes Stones Radioactive?
As mentioned above, radioactivity in stones is commonly produced by the presence of three types of minerals primarily – Uranium, Thorium or Potassium. In addition, there are a number of isotopes of phosphorus (26 through 30, and 32 through 46) can be produced artificially and are radioactive.
Radioactive stones are produced deep in the bowels of the earth, in extreme heat and pressure – within the magma layer typically. While they share many common characteristics with fluorescent rocks that develop away from UV ray exposure and tend to glow in the dark, they are fundamentally different since their isotopes undergo radioactive decay. This latter property will not be present in rocks like sodalite, which are fluorescent but not radioactive.
What Stones are Radioactive?
There are many rocks that are radioactive in varying degrees, depending on the precise composition. Metamorphic rocks are a common example.
Let’s look at them under two categories: (a) General Rocks and (b) Gemstones.
Which Commonly Found Rocks are Radioactive?
The most common varieties of rocks that exhibit significant radioactivity are as follows:
Granite, especially one of its varieties called Pegmatite, is often radioactive. Granite forms deep within the earth’s crust, erupting to the surface as magma forming rhyolite lava flows or as fine-grained ash – all of which contain glasslike particles of radioactive substances. Pegmatite contains many rare earth elements, such as monazite, uraninite and throianite, and is therefore radioactive.
2. Shale Rocks:
Shale is a sedimentary rock which evolves when normal rock formations decompose chemically, due to weathering or exposure to, and transportation by, water. The clay like deposits, which also have zeolites, have large openings where the radioactive minerals such as K, U or Th fit well. Mica and feldspar are often present.
3. Bedded Phosphate:
Deposits of bedded phosphate or phosphorite deposits form when phosphorus from seawater is incorporated in the shells of tiny marine organisms in the form of a mineral called apatite. This mineral, rich in calcium phosphate, is deposited as a radioactive biochemical sediment, given that it contains both Uranium and Thorium.
Like bedded phosphates, the hydrocarbons that make up coal contain significant quantities of Uranium and Thorium. At times, there is enough Uranium in Coal (and also bedded phosphates) for both of them to be considered low-grade Uranium ores.
Besides the ones mentioned above, a number of other stones will exhibit occasional or traces of radioactive, including sandstone (occasional) and marble (traces).
What are some Radioactive Gemstones?
Gemstones, by definition, are formed under extreme heat and pressure, deep in the earth’s crust. As such, there are dozens of gemstones that have radioactive components. Some of the ones with strong radioactivity are listed in alphabetical order below:
1. Autunite: Contains over 48% Uranium.
2. Betafite: Contains over 17% Uranium.
3. Coffinite: Contains over 72% Uranium.
4. Cuprosklodowskite: Contains over 55% Uranium.
5. Ekanite: Contains over 27% Thorium.
6. Francevillite: Contains over 48% Uranium.
7. Meta-Autunite: Contains over 56% Uranium.
8. Polycrase-(Y): Contains over 6% Uranium.
9. Samarskite-(Y): Contains over 15% Uranium.
10. Soddyite: Contains over 71% Uranium.
11. Steacite: Contains over 25% Uranium.
12. Thorianite: Contains over 71% Thorium.
13. Thorite: Contains over 87% Thorium.
14. Vandenbrandelte: Contains over 59% Uranium.
15. Yttrocrasite-(Y): Contains nearly 8% Uranium.
There are a large variety of rocks and gemstone quality stones that are radioactive; but sodalite or its close cousins are not among them. Instead, sodality has the quality of luminescence or phosphorescence, which certainly makes them glow in the dark or under ultraviolet light. Sodalite or Hackmanite do not, however, undergo radioactive decay along the lines of some of the other stones outlined above.