The Mines and Minerals of Lavrion - AlumohydrocalciteLast Updated: 9th Mar 2020
By Branko Rieck
ALUMOHYDROCALCITE, CaAl2(CO3)2(OH)4 · 4H2O, triclinic
In spring 2017 the author received a present of a piece of azurite and "picropharmacolite" as white sprays composed of fine acicular crystals up to 0.5 mm (see Figure 1) with a silky sheen. The minerals are grown on a schistose matrix and were found at the 3rd level of the Hilarion area by the local collector Vasilis Stergiou. The matrix and the paragenesis, however, made the identification of "picropharmacolite" highly unlikely. A PXRD-analysis revealed the true identity of alumohydrocalcite which was also confirmed by an additional EDX analysis. The chemical composition shows no elements present other than the main constituents. As can be seen in Figure 2, the similarity between picropharmacolite and alumohydrocalcite is indeed great. However, the matrix and accompanying minerals make it clear that this is a completely different type of paragenesis.
On the available specimen, alumohydrocalcite rests on crusts of pale blue chalcoalumite together with azurite.
Confirmed alumohydrocalcite has so far only been discovered from a single locality at the 3rd level of the Hilarion Mine. This spot is not too far from the area yielding lavendulan and kamarizaite.
Fig. 1: SEM micrograph (BSE mode) of a spray of acicular alumohydrocalcite crystals with lighter grey azurite crystals. SEM photograph by P. Marschner.
Fig. 2: White sprays of alumohydrocalcite with blue azurite on schist matrix. FOV: 4 mm. This specimen is a present from Vasilis Stergiou.
Thanks go to Dr. Uwe Kolitsch for constructive comments and diligent proofreading to improve this article.
Rieck, B., Kolitsch, U., Voudouris, P., Giester, G. and Tzeferis, P. (2018): Weitere Neufunde aus Lavrion, Griechenland. Mineralien-Welt 29 (5), 32-77 (in German).
Article has been viewed at least 957 times.