Irradiated Smoky Quartz: Is it really safe?

A lot — if not most — of the colorful quartz varieties on the market are enhanced in some way, and buyers are often none the wiser. Heated amethyst gets sold as citrine, and smoky quartz might even be treated with radiation to give it an extra impressive, uniform color.

Since a lot of crystal aficionados wear the stones and use them for healing purposes, this raises a serious question: Is it safe to use or wear irradiated smoky quartz?

How does quartz become smoky quartz?

Before we delve into this subject, it’s important to note that all smoky quartz, natural or otherwise, is irradiated in some fashion. For natural smoky quartz, this happens due to the presence of radioactive minerals in the earth. For enhanced smoky quartz, this happens after it has been mined.

Smoky quartz gets its color from changes within the crystal produced by radiation. All quartz is made of silicon dioxide, with various colors produced by mineral inclusions within this silicon dioxide lattice. In smoky quartz’s case, this is trace amounts of aluminum, which form AlO₄^– molecules that take the place of some of the SiO₄ within the crystal. If you look at the molecules, you’ll notice that AlO₄^– carries a negative charge, while SiO₄ does not. Because of this, the crystal lattice of smoky quartz also contains small amounts of positive ions, usually hydrogen, lithium, or sodium. When this quartz is exposed to radiation, some of this silicon dioxide becomes free silicon and some of the electrons from the AlO₄^– molecules get knocked out of place. They hook up with the positive ions, and create the characteristic “smoky” gray or brown color of smoky quartz.

Is irradiated quartz safe?

For the most part, irradiated quartz — whether naturally or artificially — is perfectly safe. Think of the color like a suntan. A person tans because they’ve been exposed to solar radiation, but that change in color means that radiation has acted on them, not that they are emitting radiation themselves.

Notice, however, that I say “for the most part.” After typical exposures to radiation, most smoky quartz is perfectly safe. Depending on the source of radiation, some crystals have a somewhat higher risk of becoming radioactive. It’s important to note that this is still a pretty low level of radiation, and decreases with time.

For a stone to become radioactive, radiation needs to add or remove a neutron from some of the atoms within the crystal. In other words, the energy of radiation striking the stone needs to be greater than the energy needed to bump a neutron out of place. The amount of energy it takes to do this varies by element.

Neutron bombardment using a nuclear reactor can irradiate stones, though this is a relatively uncommon method. Stones produced by this process tend to be very dark, and are almost always radioactive. Because of this, these stones are not released for sale until and unless the radioactivity had decayed to safe levels. Electron bombardment using a a particle accelerator streams a narrow beam of electrons at a stone. Many of these accelerators do not operate at a high enough energy to make a stone radioactive, but some do. Even so, the radioactivity of these stones decays quickly, making them perfectly safe within a day or two of treatment. Lastly, gamma irradiators use ⁶⁰Co (cobalt 60) to produce energy. This does not meet the energy threshold needed to make smoky quartz radioactive. In fact, this process is also used to sterilize things like produce and medical equipment.

So, what does this all mean? By the time a smoky quartz has entered the market for purchase, it’s safe. Wearing or using natural or artificially irradiated smoky quartz is not going to hurt you. If it emits any radiation at all, it will be minimal compared to natural sources of radiation that you come in contact with every day — radioactive minerals in granite, or the potassium isotopes in a banana, for example.

How can you tell if a smoky quartz has been artificially irradiated?

Unlike heat-treated amethyst, there’s really no good way to tell. Some natural varieties of smoky quartz are very dark, like morion, so you can’t always go by color. This means that, unless the stone is labeled or the dealer tells you, the only way to tell if a stone has been artificially irradiated is by examining the matrix.

Naturally-occurring smoky quartz is found adjacent to minerals that contain radioactive material. This usually means intrusive igneous or metamorphic rocks (like granite, an intrusive igneous stone). On the other hand, radioactive material is less common in sedimentary rock like shale (with the exception of uranium, which can appear in limestone, dolomite, or sandstone, among others). This means that very dark smoky quartz with a sedimentary matrix is more likely to have been artificially irradiated, though that’s not really a hard and fast rule.

Smoky quartz is a very popular and versatile stone, and it’s easy to see why — it’s as abundant as it is beautiful. Despite its abundance in nature, some stones are irradiated to improve their color, which has made some people question their safety as jewelry or healing stones. Don’t worry, though — even after getting a radiation tan, smoky quartz is perfectly safe to handle and use.