This is dolomite from the Tertiary of the Middle East. There is a whole section made up of this cross-shaped cloudy centers. Any suggestion. thanks in advance
Dear Dr. Sadooni,
These cloudy centers in your dolomite are the typical pattern of sector zoning.
The sector zoning being delineated by concentrations of inclusions.
Please find enclosed the citation of the special paper by
Reeder, R.J. & Prosky, J.L. (1986): Compositional sector zoning in dolomite. Journal of Sedimentary Petrology, 56, 237-47.
Best regards,
Guenter Grundmann
I think this is called 'hourglass texture'. I was told it originates from enclosure of solid inclusions where the crystal facets meet, during growth. I've seen them often in burial diagenetic dolomites/ankerites in clay clasts in sandstones.
Attached is an example from the Triassic of the Campine Basin, NE Belgium.
Pieter
Thank you Dr. Bertier. This sounds like a nice name "hourglass dolomite!". I was thinking of some thing like "crucified dolomite!!". regards
Fadhil
Dear Dr. Sadooni,
if you want to know more about this type of mineral texture take a closer look at the mineral andalusite, and at its variety "chiastolite". There the way how these texture comes into being is well studied and described (OM inclusions). Dr. Grundmann´s description fits best and your description I would accept. Chiastolite means "Kreuzstein" or cross stone, very crudely translated. So your terminology something like "cross dolomite" seems to be correct. I guess that Fe in its trivalent state which cannot be accommodated in the lattice of dolomite or organic material are the cause for your textured dolomite. This does not exclude any detailes mineralogical investigaton, for sure. Hourclass textures are similar and well known from ultrabasic rocks but the way of formation is different from what we might expect in your case.
Best regards
H.G.Dill
Dear Dr Sadooni,
It is also a structure seen in halite crystals when they grow as hopper crystals. I can't find the definitive article, but this one gives an example in Figure 2: http://www.deepseadrilling.org/13/volume/dsdp13pt2_22_2.pdf
Kindest regards, Tony Cooper
Dear Sir
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A similar phenomenon can also be sometimes seen in gypsum. In all the minerals where one sees this the crystal structure also has an effect. I would include the "trapiche" inclusions in emerald but because of the different crystal group it looks different.
Very useful informations , like the different answers and new terms used,but if its inclusions it will not give cross shape like that vive random shape ,it may be other phenomena and it deserve more search (Prof. Sadooni Father of carbonate and dolomite)
I want to add a 38 yr old photographic transperency and SEMicrographs of a basal Dolarenite sample from DSDP Site 217 ( which I am unable to upload).
During 1970s, Prof. Claude V Monty from Belgium and his disciples at the CFP, France, came out with a concept of Biosedimentology and Biodiagenesis - in which bacterial precipitation of layered carbonates reflecting variations Ca-Mg concentrations. A dolomite crystal in the said transparency (lower left corner) seems to be similar to that in the present discussion. Moreover, the central cores of Prof. Sadooni's sample seems to be more micritic than the cores of DSDP sample which is more sapritic. The symmetrical cross-shaped texture may be biota-specific contributing to the carbonate precipitation.
Regards to one and all.
I should hug you for this. so here is a remote hug! because this is actually what i was looking for. We are searching for indicators of microbial mediation in ancient dolomites and here you come and point to this. I am sure Jerry Friedman would be so happy to read this if he is still around. Can you please try again and upload the dolarenite sample. many thanks.
Fadhil
Dear Dr. Sadooni,
Sectorial zoning has been described for many minerals, including chiastolite (Dill), halite (Cooper), and trapiche emerald (De Fourestier) already mentioned above, as well as staurolite, chloritoid, augite, garnets, amethyst/ametrine quartz, etc. In some minerals, sectors may appear separated by solid inclusions (notably chiastolite and various trapiches), in others they may not.
Sectorial zoning may be cryptic and remain inconspicuous in ordinary petrography. Possibly, optical cathodoluminescence and/or element mapping will help reveal and coinciding chemical zoning.
Additional information may be found in eg.:
Kastner, M, and Waldbaum, DR (1968): Authigenic albite from Rhodes. American Mineralogist (53): 1579-1602. (also describing dolomite xls)
Reeder, RJ (1992): Carbonates: growth and alteration microstructures. In: Buseck, PR (editor): Minerals and reactions at the atomic scale: transmission electron microscopy. Reviews in Mineralogy (27): 381-424.
Hoping to be of help,
Maarten Broekmans
Dear Prof Sadooni,
I could ultimately send those photos to your facebook (probably to your "Others" folder) address. Please confirm so that I shall resend them, if necessary.
Regards
I think that it is a skeletal dolomite crystal followed by enrichment process.
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