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Identity HelpBotryoidal Apatite?

9th Oct 2019 23:28 BSTRobert Darabos

Found this material in a farm field about 6 months ago in Guatemala.  
I had assumed the entire thing was Hyalite Opal on Basalt/Andesite.  
The material has little to no reaction to UV lights (nothing like Zacatecas) and is typically too brittle to do a good scratch test on.  

Fast forward 6 months, I have been trying to locate Apatite from a volcanic source.  It is said to be associated with Andesitic Basalt from the Fuego volcanic complex.  
Turns out the Apatite I have been looking for I may have had the entire time and would like some thoughts and input.  

There are additional images of close ups attached to help.  
The botryoidal material in question ranges from typical glassy looking (like would be expected from Opal-An) to a white material.  I thought previously the white material was Opal-An with some inclusions.  Could this in fact be Apatite?  I am unsure if  the Apatite should react to acid or not.  If so, it does not appear to react, but the bubbles could also be incredibly small.

Below are two close up images and another image I found on the internet labeled as "Francolite and Hyalite from Czech Republic," which has incredibly similar look and the same volcanic-type rock.  

9th Oct 2019 23:29 BSTRobert Darabos

a close up of the more white-colored material and some smaller glassy botryoidal spheres

9th Oct 2019 23:31 BSTRobert Darabos

this is the image I found on the internet labeled as
"Francolite Apatite with Hyalite Opal on Andesite - from the Czech Republic"

10th Oct 2019 01:18 BSTKevin Conroy Expert

You may have chalcedony.   Try to do a hardness test in the area where the arrow is pointing to.

10th Oct 2019 01:30 BSTPaul Brandes Manager

Chalcedony would be my initial guess as well.

10th Oct 2019 02:17 BSTDoug Daniels

Note that apatite will not "bubble" with acid, it is not a carbonate.

10th Oct 2019 03:03 BSTRobert Darabos

thanks for the replies.  

the material, for the most part, is too brittle to get a good hardness test off of it.  
I can say that the solid white material does seem to scratch easier than the more glassy material.  And the brown line seems harder than both of the others.  Either way, the white botryoidal areas and the glassy botryoidal areas are brittle enough to crush from a scratch from a metal device.  I am going to look for more of the material tomorrow and will try to locate some specimens with larger surface areas to attempt a more accurate hardness test.  

I also thought the apatite would react with acid if it was like this... several sources of this material (if it happened to be apatite) said that some of the phosphate material is altered or exchanged with calcium, so i thought it could provide a weak reaction.  that was an assumption, of course, so i could be wrong.

this material is almost always found on a roadcut cliff side.  not sure when the roads were ever cut, but assumed the mineral would have to form relatively fast to occur all on the cliff sides.  with the crazy amount of rainfall here, i originally leaned towards the opal.  

10th Oct 2019 12:37 BSTAlfredo Petrov Manager

Normal apatite won‘t bubble with acid, but botryoidal carbonate-rich apatites from volcanic vugs will bubble a bit as they dissolve (of course not with the same energetic effervescence as calcite or aragonite).

11th Oct 2019 04:53 BSTDoug Daniels

Forgot about that variety.

11th Oct 2019 01:41 BSTRobert Darabos

the mineral does appear to scratch.  I tried with a piece of metal and another piece of Quartz.  
The brown-lined area was much harder to scratch.  

also could not tell if i was simply breaking the softer white / glassy material or if i was actually scratching it.  so i did a streak test and SOME of it streaks white and other parts appear to not streak at all.  albeit, difficult to get a good scratch on a clean surface.  

so maybe a mix of both chalcedony and the opal?  

assuming the original Apatite question is unlikely?  Or will need a test to be certain?
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