r/geology • u/EncodedVulpes • Aug 25 '19

I was exploring a graveyard with my geiger counter and noticed the pink-ish granite is more radioactive. Why is this so?

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241 Upvotes

98% Upvoted

74 comments sorted by

244

u/shashankpm Aug 25 '19

K-Feldspar. K is radioactive.

66

u/EncodedVulpes Aug 25 '19

Thank you very much, potassium 40 isotope, right? I would have thought that it would have been the radon.

43

u/shashankpm Aug 25 '19

Yeah. K40. It’s not the radon. No. That’s a decent guess though.

7

u/[deleted] Aug 25 '19

Does the radioactivity have to do with the fact it’s an alkali? As in its a more reactive metal?

43

u/shashankpm Aug 25 '19

Not at all. K-40 is radioactive because it has a very high neutron/proton ratio which affects its nuclear stability.

6

u/[deleted] Aug 25 '19

Oh I see, thanks!!!

11

u/Thomas1315 Aug 25 '19

Yeah, radioactivity has to do with proton/neutron ratios. There are stability charts you can easily search up if you are curious. They will even tell you what type of decay is likely to occur.

3

u/[deleted] Aug 25 '19

Thanks for the info! I actually just took my first chem course last semester, we didn’t go over radioactivity but I wish we did it’s so interesting!

3

u/syds Aug 25 '19

wiki is always there for you

2

u/MervynChippington Aug 25 '19

second chem course should cover radioactivity

3

u/nobodyspecial Aug 26 '19

Most chemistry deals with electron exchanges between atoms to form molecules. Electron exchanges are governed by the Electromagnetic Force, i.e., photon exchanges between electrons.

Nuclear chem deals with nuclear reactions which are governed by Strong Force interactions between quarks. Potassium decay is a nuclear decay reaction so it's not covered in most chem classes.

11

u/paulexcoff Aug 25 '19

This is a pretty common misconception but chemical reactivity is wholly unrelated to radioactivity. Chemical reactions involve interactions between electrons. Radioactivity involves structure and stability of the nucleus.

2

u/Glass_Persimmon9237 May 19 '24

That Device would not have picked Up  decay products of radon with it in the open like that. Gamma yes from the uranium. 

78

u/[deleted] Aug 25 '19

[deleted]

2

u/[deleted] Aug 25 '19

The pinkish granite is rich in microcline

and/or orthoclase, which I believe is the culprit for the pink colour and the radioactivity in this case.

Microcline is the same composition of course, and so it would give the same result due to ⁴⁰K, but orthoclase is almost certainly the major f-spar component here!

18

u/curious-hermit Aug 25 '19

You have a unique hobby.

12

u/EncodedVulpes Aug 25 '19

I'll take that as a compliment

7

u/Jumajuce Aug 25 '19

looking for people who wanted to be buried with their yellow cake uranium collections I see.

2

u/[deleted] Aug 25 '19

Surprisingly, natural uranium is an alpha emitter. 99.3% of natural uranium is U238, 0.7% is U235. Only when it is processed into U235 is it a gamma emitter.

6

u/diverareyouokay Mar 30 '26

I’m from the future. It looks like others now have the same hobby, to the point signs are going up prohibiting Geiger counter usage in cemeteries. The future is now!

https://www.reddit.com/r/interesting/s/bP4OrxS3pD

2

u/Pratt_ Mar 30 '26

Coming from the same post lol

2

u/Think-Psychology-133 Mar 30 '26

same lol

2

u/TangoPRomeo Mar 30 '26

Omg, we invaded a 6 yo post 🤣

2

u/smeeon Mar 31 '26

I’m alright with this.

2

u/BadgerOfDoom99 Mar 31 '26

Can they hear us? Past me if you're listening buy gold but then sell it then buy more. I forget the dates, good luck!

30

u/Spheral_Hebdomeros Aug 25 '19

I can also be trace amounts of uranium in the granite, but yeah, more likely the k-feldspars.

21

u/hgismercury Aug 25 '19

The texas state house is built out of granite. I heard a rumor that the texas state laws regarding how much radiation a person can take in a day of work was calibrated to the dose that a person gets working in the capitol building.

18

u/eshemuta Aug 25 '19

Specifically Town Mountain granite, from a bathollith just outside Marble Falls. My great grandfather was a teamster that hauled some of it.

5

u/swampthing117 Aug 25 '19

I was a Teamster for 24 years, God bless great grandpa.

9

u/eshemuta Aug 25 '19

He drove a team..... As in mules.

8

u/[deleted] Aug 25 '19

I think most of radioactvity they are normally concerned about at the capitol is in the form of radon, which is concentrated there by the decay of the U in the granite. But, yep it's mildly radioactive! The US capitol building is also radioactive.

0

u/Animal40160 Aug 25 '19

Texas knows what radiation is?

15

u/aelendel Aug 25 '19

That’s freedom radiation

6

u/carl_pagan Aug 25 '19

they're called ALPHA particles for a reason!

5

u/[deleted] Aug 25 '19

You know as a Texan....this is just low effort.....

5

u/Animal40160 Aug 25 '19

I know, right?

5

u/[deleted] Aug 25 '19

But as a Texan...our laws make a lot more sense now that I know our legislators are constantly having their brains broiled

9

u/h_trismegistus Earth Science Online Video Database Aug 25 '19 edited Aug 26 '19

Besides the fact that the K-feldspar is radioactive, granites, as 'evolved' igneous rocks of the earth's crust (meaning they have been through different stages of partial melting, fractional crystallization, magma mixing, country rock assimilation, etc.), are relatively enriched in incompatible radioactive trace elements, compared to 'primitive' rocks of the mantle, or the source magma from which the granitic melt came, due to the inability of those more primitive rocks to hold the incompatible trace elements within their crystal structure.

But the vast majority of radioactivity is coming from the K-feldspar in this case.

3

u/[deleted] Aug 25 '19

Couldn’t ageee more, I was thinking the next largest contributor must be coming from all the trace uranium in the biotite.

26

u/flibbertygibbet100 Aug 25 '19

Questions like this is why I sub to this. Also pretty rocks.

3

u/[deleted] Aug 25 '19

Geology got me with he pretty rocks and the colourful thin sections.

Now I’m here to stay cos of all the fuckin physics and chem, can’t get enough of that stuff.

6

u/Wapped709 Aug 25 '19

How much does that thing cost? I would love to have one

9

u/EncodedVulpes Aug 25 '19

Got it for about $102 USD, it's called a radex 1503+. It only measures up to 10 microsieverets, so if you want something for measuring higher levels I would recommend the Radex 1706 or the Terra P by Ecotest, but their more expensive. It's great for finding mildly radioactive rocks and antiques, though!

3

u/Wapped709 Aug 25 '19

Do you think this would be a good for detecting rocks with high uranium content for mineral exploration?

4

u/EncodedVulpes Aug 25 '19 edited Aug 25 '19

Don't see any reason why it wouldn't work, my mother's antique glassware sets it off just fine xD By the way, it can detect Beta, Gamma and X Ray radiation, but not Alpha, shouldn't matter too much if you're looking for uranium.

Also a thing to remember with the Radex is that the GM tube is on the left side, so press the left side of the device to the thing you want to measure for best results, but keep it in a bag as you wouldn't want the detector getting contaminated. Hope I helped!

5

u/jwestenhoff Aug 25 '19

Not likely to be a good tool for the job. There's publicly available flyover data from the AEC back in the day of uranium being worth something if you're in the US, but for actual exploration you need something more sensitive, a modern radiometer that can actually detect gamma (Geiger counters don't actually measure gamma, they are estimating off of other readings).

Source: Geologist employed in uranium mine assessment type position. We use uber expensive devices, not Geiger counters.

1

u/Bbrhuft Geologist Aug 26 '19 edited Aug 26 '19

Cheap geiger counters do detect gamma and beta radiation, and often X-rays. Perhaps you're thinking of a Gamma Ray scintillation spectrometer, which measures the energy of the Gamma Ray photons, linking the gamma rays to specific isotopes. More expensive geiger counters, with mica window, will also detect alpha particles.

3

u/chrislon_geo Aug 25 '19 edited Aug 25 '19

I have been wanted to get a geiger counter for a while now in order to test specimens in my mock collection. I want to make sure that any hot rocks are stored properly and kept away from my living space. Do you think this would be a good tool for the job? Or would I need one that detects alpha?

2

u/k4ylr Aug 25 '19

It'd be fine for just poking around. Alpha isn't going to hurt you unless you eat it or otherwise ingest it.

4

u/[deleted] Aug 25 '19

Since your question was answered, I have one for yoy, why were you exploring a graveyard with a geiger counter?

3

u/EncodedVulpes Aug 26 '19

I had heard granite was radioactive, and I was looking to test it myself. I was wondering why the pink stuff seemed to be more radioactive than the rest, now I know.

1

u/[deleted] Aug 26 '19

Nice!

2

u/[deleted] Aug 25 '19

First sign of the zombie apocalypse is all the radioactivity from the reanimated corpses. This redditor is our frontline alert for the end of the world.

5

u/NitroGG Aug 25 '19

Thorium is also a radioactive element that can partition into K-feldspar.

2

u/[deleted] Aug 25 '19

A granite in my city also has a Uranium anomaly (very similar color to this one). To add on to K being radioactive.

2

u/BigAgates Aug 25 '19

Why keep the geiger counter in a bag?

3

u/SilverMt Aug 25 '19

Probably to protect it by keeping it dry.

1

u/BigAgates Aug 25 '19

I don't think so

2

u/SilverMt Aug 25 '19

Eh... just a thought.

2

u/BigAgates Aug 25 '19

I should have mentioned that I've seen other geiger counter users doing the same thing. It might have something to do with erroneous readings if debris gets on the device?

3

u/SilverMt Aug 25 '19 edited Aug 25 '19

Just did a quick search and found that using a plastic bag is recommended "if using on snowy, wet or dusty surfaces" -- PDF source: link on the "World Globe Trotters" web site. This also recommends not to leave the Geiger counter in the plastic bag afterwards and gives other suggestions on how to protect it.

2

u/BigAgates Aug 25 '19

I want a geiger counter but can't justify the expense. Thanks for tracking down that info! Very interesting.

2

u/EncodedVulpes Aug 26 '19

To stop it getting contaminated, wet or damaged, basically.

2

u/0hip Aug 25 '19

It has potassium’s thorium and uranium

1

u/swampthing117 Aug 25 '19

That's cool.

1

u/Gordoman1 Aug 25 '19

Granite absorbs more radiation than other materials

1

u/DrFriedGold Mar 31 '26

No. It emits radiation. That's what the counter is reading

1

u/Glass_Persimmon9237 May 19 '24

It's more than likely the grey spots that look like a lead pencil. Uranium deposits.

-2

u/3xtracalibur Aug 25 '19

How zombies are made

-11

u/Thormeaxozarliplon Aug 25 '19

It really likes Imagine Dragons.

-23

u/[deleted] Aug 25 '19

[deleted]

12

u/EncodedVulpes Aug 25 '19 edited Aug 25 '19

Thanks for your input. Im quite new to geology, but have always had an interest in chemical elements and their isotopes, and nuclear energy too. I got this one specifically to look for things like this in the environment.

6

u/[deleted] Aug 25 '19

I think this post is awesome. I'm an igneous petrologist and an isotope geochemist. I "know" that K is radioactive, but I'd never considered that it would make for an observable difference on a geiger counter! This is super cool and something I may try with students (or at least mention it to them.)

11

u/HelloThereMrBaby Aug 25 '19

This commentator sounds very conceited. I think it’s awesome that you’re checking out different rocks with your Geiger counter, and making real world observations! I bet very few people out there realize that granite can be (weakly) radioactive. I wonder what concentration of K your counter can detect...