It is a vuggy a oligo- to polymictic breccia/conglomerate cemented with carbonates, lacking any pronounced bedding or typical vein structures. It looks like a carbonate sinter be it hydrothermal or not. It should be of young geological age, maybe Quaternary or Neogene. If sedimentary processes were involved they should be colluvial (alluvial) in origin. That is my rather vague image interpretation.

With kind regards

H.G.Dill

Harald's interpretation is likely, I however see more evidence of a likely ancient alluvial deposit(especially the embedded conglomerates) which may likely be relatively younger in age perhaps as suggested by Harald. Although you were doubting on to whether the rocks are "old volcano", it may be possible if the area has once being occupied by such rocks to have form part of the alluvial sediments. I suggest you observe the rock in hand specimen to see whether it is a weathered volcano (siliciclastic sediments stands out from crystalline rocks even when weathered), secondly I will suggest that you study the field relationship of the rocks in the area to see how this rock relate to other rock types.

Good luck on your quiz.

Dear Michael,

The description of Mr. Dill is absolutely plausible. Nevertheless, I would like to present an alternative explanation with respect to a possible volcanic origin of the rock. I see a fine-grained matrix (if it's not carbonate sinter), rounded and more angular components, matrix-supported, no clear stratification, no sorting, no grading. Accordingly, it might be feasible to interpret these rocks as deposits from a Lahar, following a volcanic eruption. The carbonate veins might be the result of secondary carbonate precipitation induced by hydrothermal processes.

But I have to point out (in accordance to H. Dill) that this is a really vage interpretation of your images.

All the best,

Elmar

Thank you professors Dill, Mohammed and Buchner for your constructive suggestions.

I should have included a picture of the so-called "castle", the prominent steep-sided hill that this rock makes in this area. The geology map of the island roughly includes this area into a sedimentary sequence, but there are no detailed maps that I could find.

Looking from a distance one would say this hill must be an old volcano!

After going through above comments made by Harald G. Dill , Mohammed Mohammed and Elmar Buchner , it looks for me as travertine is country rock with other fragments.

I would not hazard a guess based on photos and a brief description. I believe it is very necessary to go out in the field, visit the site and its surroundings, and take samples for mineral analysis and, if possible, for isotopic dating.

At first glance, this looks like travertine to me. The statum shape on the photo, the highly porous texture, obvious botryoidal shapes in some of the images, features of flowing, crusts, and the abundance of calcite, all this togheter leads to assumption about hydrothermal, hot spring travertine. It is very promising for epithermal system in depth.

Regards,

Irina

For me, it looks like Caliche.

The pictures alone can infer lots of assumptions quickly...i could see footprints of erosion, weathering, dissolution, clasts , etc...so there may be need to understand the geological story and put all observations in to perspective before arriving at a definitive conclusion......

This rock is Calcite ( CaCO3 )

Dear all respondents Teslim Adeleke Basant Bhandari Hafizullah Rasouli Irina Marinova Jeffrey Paul Schaffer Ijaz Ahmad, Elmar Buchner, Mohammed Mohammed, and Harald Dill,

Thank you very much for your constructive comments and valuable observations trying to solve the rock identity in this case.

Although the geology of this island has been covered in general terms and in great detail in some parts, others- like the case of the "castle"- have not received much attention (that I could find).

Looks to me like a polymict pebbly sandstone with a carbonate rich matrix/cement. Weathering has apparently been moving some part of the cement around probably judging from the shapes of the hand specimens and the calcrete/travertine on some faces. A scale on the photos would have helped a bit as well. If you zoom in on the pictures you can see many rounded grains, some that have a flat face and rounded edges as well. indicates fluvial or marine transport, could be related to a hot spring but that would appear to me to be an unnecessary added complication.

Dear Peter Temby and @ Elmar Buchner,

Thank you both for your constructive observations and comments.

The hot spring travertine situation would explain the textures observed, but there still remains the steepness of the geographical feature that stands tall compared to the surrounding rocks.

Dear Michael Issigonis

Related to the petrology interpretation, look in a gray color to white so determine of the some resistance mineral and evaporate mineral. Vuggy porosity consist in this body rocks of sample. Some Mineral alteration in some body. related to the granule or nodule that see in this body of rock i consider it related some litic and mineral that inclusion to this rock. Related to the position be in the contact of the rocks. related to all body of sample it related to the Sedimentari carbonate rock. or Limestone. And also must be go to the field to check country rocks.

To give name I think continue to the Petrograpy analysis in thin section or other method to related. Thanks Michael Issigonis

And also i think it will be reefs (belong to oceanic rocks)

The prominent hill appears to have a flat top and may be an isolated remnant of the peneplanated surface seen on the hills in the background. Maybe there is a hard duricrust present on this surface or possibly, if it is flat lying, a durable sedimentary unit.

Dear Peter Temby

The attached is the west side of this hill. Almost vertical and smooth face showing a network of whitish "channels" presumably calcite. It shows fractures, but has to be very durable rock.

Looks like tufa variety of travertine.

Thanks Michael

the sequence is a moderately dipping sedimentary sequence as far as I can see and the whitish rock looks very much like travertine or calcrete remobilised into a major joint or fracture surface, similar to the carbonate on the surface of the rock in a . the top would almost certainly be a planation surface given the dip on the bedding evident in the photo.

Thank you Peter for your contribution. I can see that the whitish rock (travertine) acts like cement in the fractured rock and keeps it standing up like a fort - very impressive natural structure from the distance.

It certainly is a very interesting looking feature in the landscape, no wonder its referred to as the Castle. Must be a great view from on top.

This is the view from the top on 2 sides.

Dear Mr. Issigonis,

I used your attached photograph and made an interpretation of this fractured and tilted limestone complex which underwent karstification with its solution cavities controlled as to their emplacment by structures cutting the fault plane obliquely-

The stylolites, bedding planes and the orientation of the karst cavities reflect the original position of the sedimentary unit prior to tilting (see dip).

With kind regards

H.G.Dill

Nice detailed analysis Harald.

There is reefs (fringing, Barrier and atoll)

Thank you @ Harald G. Dill so much for making the local geology easy to understand.

I am amazed why my answer has been deleted.

Dear Ijaz,

If you mean your answer of Nov. the 11th, it is still there, under "show previous answers".

Looks like a highly indurated caliche Or calcrete. The vuggy structures reveal secondary solution actions. The occasional quartz, pebbles perhaps reveal involvement of external surface sources during lithification.

I agree with H.G.Dill . From the photos you give in the field, it's really like the latest diluvium or flood fluvial deposit. The age is very new, it's not consolidated into rock, and it looks like the existence of calcium cement.But whether there is the composition of volcanic ash needs further analysis.

LIu

Dear Ramesh Chandra Phani ,

Thank you for your explanations. There is a lot of cavities during this secondary invasion of fluids. The rounded pebbles of quartz have a variety of colours suggesting an origin of various sources of material during this action.

Dear Liu Chenming ,

Thank you for your valuable interpretation. I will do some analysis to help in the identification of this rock.

Hard indurated calcrete? Moreover, its with a few pebbles visible in photographs, may be of quartz, and carbonate as cementing material in hard form as appearing in vuggy structure.

Looks like travertine.

I think its a well-cemented sandy conglomerate made of polygenic clasts, covered by a carbonate crust, maybe travertine (fig 1-2).

Looks like marlstone. Does it react with HCl solution?

Plenty of really good suggestions. I have some minor comments:

The clasts are not entirely quartz. Lithic fragments, ranging in colour from grey to greenish and black are more abundant. A few are reddish brown. They show quite a range from rounded to angular. No doubt they are cemented by carbonate. I wonder if the "conglomerate" is only surficial and deep down the rock is a homogeneous (?)carbonate.

Thank you Anzor Giorgadze for your suggestion. Yes, definitely lots of calcite reacting with the acid.

Thank you M. Qasim Jan for your comments and suggestion. There is indeed quite a range in colors and shapes of these stones. I did not see outcrops of this rock in lower slopes, only other sedimentary formations. So this "travertine", as many people called it, looks like a volcano.

Dear Angelo Cipriani

Thank you for your interpretation and suggestion. The class seem to be scattered throughout, not a particular layer.

Dear Golonka Jan Atul Kohli

Thank you for your contributions. The rock seems to be very hard, although it is made of calcite and sticks out like a volcano. The surrounding (?) rocks are softer sedimentary formations on the lower slopes of this small mountain.