What Makes Smoky Quartz Black?

Did you know that only some of the smoky quartz on the market is natural?

That's right... Some crystals are pulled out of the ground in all their black/gray/brown glory!  And some smoky quartz crystals came out clear, were sent off to a lab- and returned as smoky quartz. 

As a crystal buyer you might want to know if that smoky quartz crystal you're drooling over (and about to add to your cart and collection) is natural or modified in a lab.  Now you at least know to ask. 

If you're curious about what gives smoky quartz its dark look- how the process works- both in the ground and in the lab- this blog's for you!

Colors of quartz

Smoky quartz is just one flavor of quartz. There's also rose quartz (and if you're wondering why that's pink you can read about it here), pink quartz, amethyst (purple), citrine (yellow-brownish), prasolite (green- also super rare), milky (white), blue (also rare) and clear quartz.

Quartz Composition & Colors

Every one of them is SiO2- that's two Oxygens for every one silica.  Sometimes tiny amounts of other elements sneak into the crystal lattice or swap out for a silica and cause color variations. OR sometimes inclusions of fluids or other minerals impart the color. 

So what is smoky quartz?

Smoky quartz includes crystals as dark as midnight and completely opaque (also called morion) to an ever so slight tinge of transparent gray or brown.

This picture shows a translucent (light gray) smoky quartz crystal on the left and a completely opaque deep black morion quartz crystal on the right. 

Sometimes clear quartz has bits of black or gray shale inclusions within its crystal structure. From a distance the crystals may look like smokies, but up close you can see little "floaters" within the crystal. These are NOT smoky quartz.

It's also sometimes (mis)spelled as smokey quartz- but none of my mineralogy texts have that extra e.  (Seriously, no judgment though. I was runner up *not winner* in the 3rd grade spelling bee.  Thanks to the word "biscuit" and that whole humbling experience, I'm no longer a spelling snob.)

How does smoky quartz form?

A clear start

It starts out like any other clear quartz crystal. Literally.  Nice quartz crystals grow as hot, silica rich fluids circulating deep underground in open veins/fractures precipitate quartz. (We're not talking about the little quartz crystals in an ordinary granite here. Those form by a cooling magmatic body.)

If there's enough space, water in the fluid and time - large, well formed crystal clusters and points form. And if they crystallize too fast and are a bit cramped, massive "chunky" quartz results - lacking the nice crystal shapes.

General structure of quartz

The Silica and Oxygen atoms of quartz bond to form tiny tetrahedrons.  Each Silica hooks up with with 4 Oxygens as shown in the cartoon in the figure above.  The SiO4 tetrahedrons form chains (sharing the Si atoms and keeping the ratio at SiO2). 

2 special things needed for smoldering smokies

That clear quartz needs two things to turn smoky.

1. Aluminum  Smokies require aluminum atoms in the crystalline structure.   Remember, two Oxygens for every one Silica are the main building blocks of quartz.  Sometimes, Aluminum atoms substitute for Silica atoms. Smoky quartz has up to a few thousand Aluminum atoms per million silica atoms (Rossman, 1994).  They form AlO4 tetrahedrons.

2. Irradiation   When a clear quartz crystal (with some Aluminum - as described above) is exposed to irradiation, the Oxygens bonded to Aluminum atoms change valance states to balance the Aluminum.  Those oxygens release an electron associated with the Aluminum 3+ ion substituting for the Silicon 4+.  Stranded electrons in the crystal lattice cause absorption of light waves.

In the ground

In nature, low levels of radioactive decay occur in the Earth's crust.  After minerals form in the Earth, they tend to hang out in the ground for a looong, long time (on the order of millions of years to hundreds of millions of years). 

Until eventually they become exposed at the surface of the earth and picked up or dug out by a crystal collector.  During this stint, minerals are exposed to low levels of natural radioactive decay in the surrounding soils as feldspar minerals break down to clays.

This is how clear quartz (with Aluminium traces, ofc) turns to smoky quartz in nature.

In the lab 

Clear quartz crystals bombarded with high levels of radioactive decay (usually Gamma radiation) in short doses in a lab turn smoky. Irradiating minerals is a common practice in the gemstone industry. Radiation (often combined with heat treating) imparts colors on all kinds of minerals including, quartz, diamond and topaz.

U.S. laws require gemstone sellers to disclose heat, radiation and other treatments.  However no such laws exist for specimen crystals.  Also, there's plenty of unregulated crystal selling going on. Seriously, every day on IG I get a new follower often with a DM- who's an overseas wholesale mineral dealer that accepts PayPal.  Who regulates those kinds of purchases? No one.

How to tell if your smoky quartz crystal has been irradiated

I have a friend who worked as a career gemstone cutter.  He has an uncanny ability to detect irradiated minerals. It's like his 6th sense. But if you don't have a built-in ability to sniff out irradiated minerals like this guy, there's a few ways you can figure it out.

1. Ask the seller

2. Know where its from - in the US, smoky quartz crystals are notoriously found in the Rockies of Colorado, Utah and New Mexico.  They're also found in the NE U.S. mountains - from Maine, through to West Virginia. Smoky quartz is the state stone of New Hampshire.  Natural smokies are super rare in Arkansas compared to the very common clear quartz. So if you find gorgeous (affordably priced) smoky quartz from Arkansas - ask if it's been processed in a lab.

3. Lab testing - It's possible to send material off to labs to test for any alteration (heat treating, irradiation, etc.). But really, who's going to spend $500 on testing for a $100 smoky quartz point?

Truth Minerals smoky quartz source

Looking for a truly natural quartz crystal? Every smoky quartz crystal in our shop came out of the ground with its black tint.  Some of them are so black and opaque you can't see through them and others have a faint gray tint. But none of them took a trip to a lab.

Each one was hand extracted from the Colorado Rockies.  And hand selected by us directly from the miner.

So whether you're looking for a stone for your grounding practice or just love the look and feel of these dark crystals, you can't go wrong with our selection.  Check them out here.

References

Rossman, George R., 1994, Colored Varieties if the Silica Minerals in Reviews in Mineralogy and Geochemistry, Volume 29, Chapter 13

Weldon, Robert, GIA article: An Introduction to Gem Treatments (https://www.gia.edu/gem-treatment)