The second photomicrograph is from Stoppa et al. 2019.

Dear Ioannis, there is insufficient information to make that call. The best practice of identifying a rock is to identify the constituent minerals. Once the mineral composition is known, then the classification really just comparing the mineral percentages to the classification tables. Carbonatite contains a fair amount of calcite, so if the white patches on the first photo show the typical birefringence colours in cross-polars, then perhaps it is a carbonatite. However, it could just as well be a carbonate sedimentary rock. It is not uncommon that island arc complexes have both volcanic and sedimentary rocks interbedded. If it is a volcanic rock, then it appears that the vesicles are lined with secondary minerals (chlorite or smectite group minerals?). A subduction or obduction environment is not really conducive to form carbonatite magmas.

Synthesis of Literature and Field Work Data Leading to the Compilation of a New Geological Map—A Review of Geology of Northwestern Greece

Dimitrios Ntokos, 2017. According to this paper, the Pindos is mainly flysh with some andesitic volcanics, so your rock is likely to be a carbonate (NOT carbonatite).

DEAR JOSEF

GOOD MORNING AND THANK YOU FOR YOUR DETAILED REPLY. A TOP VOLCANOLOGIST THAT SAW THE SAMPLES AND THIN SECTIONS TOLD ME THAT HE IS SURE IT IS A GEYSERITE. HOWEVER THE SIMILARITY WITH ITALIAN CARBONATITES IS TOO STRIKING. NOTE THAT THE SAMPLES WERE FOUND IN CRATER WITH A RING (SEE NEW PHOTO ATTACHED).

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IOANNIS

Interesting. From a distance, on a photo, it is difficult to see. The white bits could be cryptocrystalline silica and it would also account for the vugs/pores, so geyserite is an option. However, the aerial view photo doesn't look like showing a crater or a series of craters. They look from the distance as karst features (dolina), not uncommon in the limestone-flysh sequence. Karstic features seem to be also exposed in the top left corner of the photo, on the far side of the stream. Of cause your local colleague would have a tremendous advantage in the identification to perform the typical physical tests one would do to identify the minerals, which is still the key for the rock identification. It would be rather easy to distinguish limestone fragments (calcium carbonate, hardness 3) from cryptocrystalline silica (hardness 7), just by scratching the hand specimen.

DEAR JOSEF

I SEND YOU ANOTHER AERIAL PHOTO WHICH IS CLOSER AND YOU CAN SEE THE RING. KARSTIC FORMATIONS LIKE DOLINES LACK RINGS. ALSO THE VOLCANOLOGIST SAID THAT THE SAMPLES CONTAIN FRAGMENTS OF LIMESTONE AND ARE SILICIFIED.

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IOANNIS

Hi Ioannis, nice aerial image. Interesting to see the concentric internal ring structures below the water level. I am less than convinced that what we can see around the lake is a miniature maar ring, the scale is just not right. Can't dispute it from far afield, but it doesn't look right. The depression between the surrounding ground and the "rim" could form by other means as well, such as erosion. On the previous photo a long slope, forming a large catchment is indicated. Another interesting feature that the aerial image shows is the concentrical feature on the upslope side of the lake. It looks like an incipient solution dolina forming just upslope from the two older ones. How come the water colour is so different in the two adjacent lakes? What is causing the dark reddish tones in the upslope one, would it be terra rosa? Anyway, I think we established that it is not carbonatite. I will let you work it out whether it is geyserite or just silicified limestone. Silicification of carbonate rock is not uncommon if they are exposed to silica saturated fluids generated by metamorphism due to tectonic movement. Good luck with it, you may need to go back on another holiday to the mountain to look for the rocks in the adjacent areas as well:)

Dear Ioannis: Volcanic carbonatite doesn't contain calcite at all, the one erupted by Ol Doinyo Lengai volcano, in Tanzania, is made of two alkali cabonates, nerereeite and gregoryite, both carbonates of Na and K, with very little Ca. These crystals are prismatic and elongated, anjd have wonderful high order colors of birrefringence. What you have, certainly, it is not a natrocarbonatite, I happen to own two small samples of this rare and unique lava from Tanzania, in my collection. With only one photomicrograph I'm unable to tell which rock it is, but it looks as a kind of carbonate breccia, or the like. Regards, Sebastian.

DEAR JOSEF

GOOD MORNING AND THANK YOU FOR YOUR DETAILED REPLY. I AM SENDING YOU THREE MORE PHOTOS FOR YOU TO DECIDE. THE FIRST IS THE CRATER UP CLOSE, THE SECOND IS A DARK SAMPLE WHICH IS VERY COMMON INSIDE THE CRATER'S RING AND THE THIRD IS A VESICULAR BRECCIA FOUND JUST OUTSIDE THE RING. PLEASE COMMENT.

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IOANNIS

DEAR SEBASTIAN

GOOD MORNING AND THANK YOU FOR YOUR INTERESTING REPLY. THERE ARE VOLCANIC CARBONATITES CONTAINING CALCITE IN ITALY (STOPPA ET AL. 2019), NAMIBIA, ANGOLA, THE CAPE VERDE ISLAND FOGO AND ELSEWHERE. YOU CAN CHECK THE FOUR VOLUMES OF "ALKALINE ROCKS AND CARBONATITES OF THE WORLD" EDITED BY ALAN WOOLLEY. THERE IS ALSO A META-CARBONATITE DIKE CONTAINING CALCITE ON THE PIERIAN MOUNTAINS OF GREECE (SCHENKER ET AL. 2018). I HAVE ATTACHED SEVERAL PHOTOS TO THIS QUESTION. I ATTACH TWO MORE PHOTOS. THE FIRST IS THE META-CARBONATITE DIKE ON THE PIERIAN MOUNTAINS OF GREECE AND THE SECOND IS A NEW BUT DIFFERENT PHOTOMICROGRAPH. PLEASE COMMENT.

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IOANNIS

Dear Ioannis: surely I know about Italian calcitic carbonatites, I also have a sample fo those..., but they are not lavas, but dikes intruded in volcanic terrains. Another carbonatite dike I have seen is intruding the alkaline volcanic complex at Kaiserstuhl, near Freiberg, in southern Germany, in the Rhine Graben. Same happens in Cabo Verde, Angola and Namibia. They are late dikes intruding volcanic complexes, not lavas. True volcanic carbonatites, like those at Ol Doinyo Lengai, in Tanzania, are natrocarbonites, and form lava flows and tephra. The carbonate vein in the amphibolite-epidosite unit you show in the attached photos is really a metasomatic vein, not an igneous dyke. They used to be called "ophicalcites" in the old literature, I doubt really that is a true igneous carbonatite... or metacarbonatite. Regards, Sebastián.

DEAR SEBASTIAN

GOOD MORNING. THANK YOU FOR GIVING ME THE CHANCE TO DISCUSS A MUCH DEBATED MATTER. THERE ARE AT LEAST 48 EXTRUSIVE (VOLCANIC) CARBONATITES APART FROM OLDONYO LENGAI (WOOLLEY & CHURCH 2005). EXAMPLES ARE THE GROSS BRUKKAROS VOLCANO (KURSZLAUKIS & LORENZ 1997) IN NAMIBIA AND THE CATANDA VOLCANO IN ANGOLA (CAMPENY ET AL . 2015). NO LAVA FLOW IS NEADED FOR A CARBONATITE VOLCANO TO OCCUR (E.G. DIATREME VOLCANOES). THE PIERIAN MOUNTAINS META-CARBONATITE DIKE DOESN'T LOOK LIKE AN OPHICALCITE (SEE ATTACHED GREEK OPHICALCITE PHOTO FROM LARISA) AND IT ISN'T ONE SINCE THESE ROCKS HAVE A MAGMATIC (MANTLE NOT CRUSTAL) SIGNATURE IN THEIR CARBONATE (SCHENKER ET AL. 2018). EXTRUSIVE CARBONATITES GENERALLY APPEAR IN CONTINENTAL RIFTS LIKE THE RIFTING OF THE PELAGONIAN ZONE ON THE PIERIAN MOUNTAINS. PLEASE COMMENT.

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IOANNIS