Philipsburgite with a low phosphate content [later recognised as goldhillite] from mine Tripoli (Almeria, Spain)
21st Sep 2017 16:47 UTCAdolf Cortel
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During one of the explorations of the mine Trípoli (Barranco del Cura, Huércal de Almería, Almería, España) a mineral, which finally was identified as philipsburgite, appeared. The description of the deposit and the analytical techniques used have been described in :
http://www.foro-minerales.com/forum/viewtopic.php?t=12571,
http://www.foro-minerales.com/forum/viewtopic.php?t=12573
http://gr-mulhacen.foroactivo.com/t1952-philipsburgita-barranco-del-cura-huercal-de-almeria-almeria-andalucia-espana?highlight=cura
Since these web pages are in Spanish, it seems opportune to write an English description, which will be useful for much more mineral amateurs, of how philipsburgite with a low phosphate content, the most interesting mineral from this mine, has been identified. Furthermore, a short description of the location and the species found in this mine can be found at the mindat page:
https://www.mindat.org/loc-294173.html
The analysis of the collected samples by means of LIBS (Laser-Induced Breakdown Spectroscopy) and Raman spectroscopy revealed that besides very common minerals as dolomite, malachite, chrysocholla and conichalcite, and not so common, as cornwallite, there was another mineral in the form of a crystalline green-emerald crust over dolomite, sparsely covered by malachite.
The pictures of the mineral (as the following one, taken by Josep A.Soldevilla, and the images from a SEM) show how its appearance is similar to tiny bricks or planks irregularly piled.
LIBS showed that it was a copper arsenate with some copper replaced by zinc. The arsenate symetrical stretchig signal was the most prominent in the Raman spectrum, however no coincidences were found searching in the RRUFF database. A more accurate search in the original bibliography revealed an acceptable coincidence with the Raman spectra of philipsburgites with a low phosphate content, which have been described by:
Ciesielczuk, Justyna & Janeczek, Janusz & Dulski, Mateusz & Krzykawski, Tomasz. (2016). Pseudomalachite-cornwallite and kipushite-philipsburgite solid solutions: chemical composition and Raman spectroscopy. 8th European Conference on Mineralogy and Spectroscopy (ECMS). 555-569. 10.1127/ejm/2016/0028-2536.
Thanks to the kindness of the Grup Mineralogic Català (GMC) the mineral was analyzed by means of SEM/EDS, giving the approximate chemical formula Cu4.5 Zn1.5(AsO4)2 (OH)6. If was confirmed the very low content of phosphate (atomic ratio P/As< 0.07) suggested by the lack of phosphate signals in the Raman spectrum; even at some points of the sample phosphorus was undetected by EDS. The phosphorus was also undetected in another SEM/EDS analysis kindly carried out by Ramon Jiménez (Instituto Geológico y Minero de España).
Finally the identity of philipsburgite was confirmed thanks to Jesús Franquesa by means of powder XRD at the Serveis Científico-Tècnics de la Universitat de Barcelona, within the agreement between the University and the Grup Mineralogic Català.
The results available point to a very low content of phosphate relative to arsenate. If this low proportion (atomic P/As <0.07) is confirmed, of all the philipsburgites found so now, this one of the Tripoli mine will be the one with lowest phosphate content ever found, and the nearest to the arsenate end in the series philipsburgite-kapushite. Much lower than the one keeping the “record” (Yamato mine, P/As=0.22).
Many thanks for the help of Josep A. Soldevilla, Grup Mineralògic Català, Ramón Jiménez and Jesús Franquesa. The community of mineral amateurs are indebted to the tireless APGA members for his task, and particularly to José F. Castro who has generously provided for all the samples needed for the analysis.
Finally the identity of philipsburgite was confirmed thanks to Jesús Franquesa by means of powder XRD at the Serveis Científico-Tècnics de la Universitat de Barcelona, within the agreement between the University and the Grup Mineralogic Català.
The results available point to a very low content of phosphate relative to arsenate. If this low proportion (atomic P/As <0.07) is confirmed, of all the philipsburgites found so now, this one of the Tripoli mine will be the one with lowest phosphate content ever found, and the nearest to the arsenate end in the series philipsburgite-kapushite. Much lower than the one keeping the “record” (Yamato mine, P/As=0.22).
Many thanks for the help of Josep A. Soldevilla, Grup Mineralògic Català, Ramón Jiménez and Jesús Franquesa. The community of mineral amateurs are indebted to the tireless APGA members for his task, and particularly to José F. Castro who has generously provided for all the samples needed for the analysis.
After my first post, a few days ago, on the philipsburgite of Tripoli mine, a differential scanning calorimetric analysis (DSC) of a sample of this mineral was kindly made by M. Beltran. Since I've unable to find a previous thermal analysis of philipsburgite I provide the spectrum in case it could be useful to others.
This spectrum is similar to the ones of agardites described by Frost, Ray and Erickson, Kristy and Weier, Matt and McKinnon, Adam and Williams, Peter and Leverett, Peter (2005) Thermal decomposition of agardites (REE) –relationship between dehydroxylation temperature and electronegativity. Thermochimica Acta 427:pp. 167-170.
Since both agardites and philispurgite are highly hydroxylated but the content of crystallization water is low, the comparison of both spectra suggests that the complex main signal observed in the DSC spectrum of philipsburgite could be due to dehydroxyilation and the ones at lower temperature are due to dehydratation,
This spectrum is similar to the ones of agardites described by Frost, Ray and Erickson, Kristy and Weier, Matt and McKinnon, Adam and Williams, Peter and Leverett, Peter (2005) Thermal decomposition of agardites (REE) –relationship between dehydroxylation temperature and electronegativity. Thermochimica Acta 427:pp. 167-170.
Since both agardites and philispurgite are highly hydroxylated but the content of crystallization water is low, the comparison of both spectra suggests that the complex main signal observed in the DSC spectrum of philipsburgite could be due to dehydroxyilation and the ones at lower temperature are due to dehydratation,
