Apatite - Radioactive??

[Rex Allers]

That is a strange looking rock.

Made me wonder if this kid could be involved?

[ccipp]

Went up to visit Bill Kolb for 4 days. We did a lot of show and tells of various goodies. Virtually all 4 days were doing gamma ray spectrographs, minor activations and other nuclear related activities.

I purchased a rock ostensibly collected from the Shenandoah valley out near Roanoke from a local rock shop. It is quite radioactive over all of its surface. (photos attached) The main reason I bought it is its unusual "spatter" patterns all over it. How was this rock formed? Not sedimentary for sure. It as if in the molten state, something, also molten, spattered into the matrix.

The black streaks contain Uranium. The overall orange-brown shows up as monazite with thorium. The gamma spectrum indicated both minerals were there, contributing to the overall radioactivity. We got some peaks that were not attributable to either. Bill is going to run a long term analysis with some piece we chipped off the rock.

I also had Bill take a photo with my foot on his monster find rock from the home stake mine shown above.

Richard Hull

Nothing strange about it. That's a typical way a contact metamorphism skarn looks like. It occurs at the contact between granites and limestones, in this case likely a dolomite (Ca & Mg carbonate). The elongate crystals is tremolite that is a type of amphibole (Fe and Mg rich in this case due to the dark color). The amphiboles themselves do not concentrate U and Th, but can host Uranium minerals, like zircon and apatite.
Ciprian P.

[ccipp]

Thanks Jim for the paper PDF.
Phosphates combine in weathered Uranium. To make urano-phosphate compounds. very common.
Cool nodule image.

Richard Hull

There is a very complex interrelationship between U and phosphates. In order for uranium to be "collected" into apatite it needs a reductive redox environment that translates into low concentration of O2 dissolved in the water. The previous statement implies that we are talking about sedimentary precipitated phosphates in this case, so one also needs to add that there are various types of apatite. They are of igneous, metamorphic and sedimentary origin. All of them can have various amounts of U. The latter type (sedimentary) can gather the most of U.
Most of the sedimentary apatite (also referred to as phosphorites) form from the decaying of dead animals (vertebrates). Thus phosphorus comes from the bones, and U form the water basin where those animals died. The decaying flesh of those animals has a reducing effect on Uranium (meaning it consumes the oxygen in the water) , turning it from U6+ to U4+, ready to be used to form the apatite. Moroccan phosphorites are formed this way, and that is why they are sometimes very rich in uranium.
Apatite also concentrates more in certain igneous rocks. Igneous rocks tend to be more enriched in Thorium though, in minerals such monazite and xenotime. These minerals form close to apatite, leading to the false impression that it is apatite that is the radioactive source.

[Richard Hull]

I purchased apatite from 5 different dealers at a number of rock shows. some claimed far off origins for their material. I do not know if any was from Morocco though. However, all of the various specimens I obtained, using Gamma ray spectroscopy, indicated only tramp thorium and no Uranium content (radium daughters).

Apatite is very inexpensive, so I tend to pick up samples at every rock show and test them using my gamma ray spectrograph gear. Thus far, only a thorium signature is seen.

Finally, please never used quote blocks in replies in these forums. We consider them needless and a sign that the replier feels we are ignorant and have not read all the foregoing material. Please do not embarrass us by using quote blocks from past posts in your replies.

Richard Hull

[ccipp]

Hi Richard,
I guess many of us are using the forums on auto pilot never having a second thought about using the quotes, just to underline to whom are we replying to. If using quotes is a rule I have broken, there's no excuse on my side as I seldom read all the rules in a forum.
Getting back to the apatite topic, apatite it is not expensive indeed. However, unless one makes chemical analyses to confirm the presence of Ca, P, O, Cl and/or F, there is hardly any good reason to classify the pictured samples as apatites.
It is also hardly a wise decision to diagnose minerals from a simple picture, but I'll give it a try anyway.
So, I'd say that the bluish samples are more likely copper phosphates (Turquoise) or copper silicates (chrysocolla).

[Jim Kovalchick]

Speaking of rules, real names are required on this forum. Take note that we are all using first and last names. I get it that you rarely read rules of forums, but to be honest that sounds disrespectful even though I assume that wasn't your intent.

Thanks for sharing your knowledge here.

Jim Kovalchick