I agree with Diego, Look in this site for SEM images of marcasite      https://www.google.it/search?q=marcasite+sem+images&biw=1093&bih=479&tbm=isch&imgil=aAGrWS2ovFtTqM%253A%253Bd2BTfiJIwgnFXM%253Bhttp%25253A%25252F%25252Fjsedres.geoscienceworld.org%25252Fcontent%25252F81%25252F7%25252F447.figures-only%25253Frelated-urls%2525253Dyes%25252526legid%2525253Djsedres%25253B81%25252F7%25252F447&source=iu&pf=m&fir=aAGrWS2ovFtTqM%253A%252Cd2BTfiJIwgnFXM%252C_&usg=__Y3q9giG581e8RN5AjPYm1r8bHQw%3D&ved=0CDgQyjc&ei=MM8rVMvQK8LzPKyogBA#facrc=_&imgdii=_&imgrc=aAGrWS2ovFtTqM%253A%3Bd2BTfiJIwgnFXM%3Bhttp%253A%252F%252Fjsedres.sepmonline.org%252Fcontent%252F81%252F7%252F447%252FF7.small.gif%3Bhttp%253A%252F%252Fjsedres.sepmonline.org%252Fcontent%252F81%252F7%252F447.figures-only%3B200%3B200

Dear Muhammad,

I'm also not a SEM specialist. But have considered relating SEM images results with micromorphological analysis?

https://www.researchgate.net/publication/240788917_Micromorphological_and_Submicroscopical_Features_Related_to_Pyrite_Oxidation_in_an_Inland_Marine_Shale_from_East_Central_Saskatchewan1

http://www.publish.csiro.au/paper/SR98113.htm

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2389.1970.tb01172.x/abstract

Hope it helps.

Cheers

JAG

Article Micromorphological and Submicroscopical Features Related to ...

Since you are obviously working on a non-flat surface your EDS signal is not very reliable. Did you take this into account? Only because you get a signal it does not matter it is coming from your beam position. The backscattered electrons may also generate a very strong signal. What is the surrounding material?

Dear Muhammad,

You have already received very nice answers and good suggestions from Joao for related publications. It seem clear from the photo that the crystals morphology is not of pyrite and I agree it is of marcasite.

Just a short answer to Gert - the surrounding sediments of such kind of Fe-sulphides are so different in composition that it is not possible to be mistaken. 

Dear Muhammad,

I also agree with the proposals of being marcasite. Does not look pyrite having that habit.

Mirka, I do not doubt an assignmanent of marcasite instead of pyrite, but if it is a non - flat surface he needs to see some other elements as well, and then I would be interested in the quantification of the entire signal. My general point is only that EDS on a non - flat surface cannot be a strong proof. 

Yes, Gert, you are right about that. Quantitative chemical analysis cannot be a proof here. For sure it should be combined with other techniques. Fortunately the shape of the crystals is quite indicative for marcasite, which can help a lot. If it would be possible to prepare sulphide concentrated sample and make x-ray diffraction analysis, the presence of marcasite can be confirmed. 

...or one would make and EBSD pattern which is possible if not everywhere shaddowing appears. Usually the quality of such pattern is not that bad. However, it needs a bit experience since working under 70 tilt with a non-flat sample can be challenging.

Thanks everyone for nice suggestions. It is helpful.

Dear Gert, the surrounding material is mainly clay minerals.

Dear Muhammad,

FeS2 occurs in two polymorphic forms pyrite and marcasite. What is shown om your photo looks laike marcasite. I would advice you to make a good polished section in order to reveal what sits inside your globular form which only on the surface can be covered by marcasite but inside it can be framboidal pyrite globe. This tye of texture is called sunflower texture and please consult Ramdoh's famous book on Rock forming minerals and their intergrowths. 

Concerning trace element chemistry there is usually difference in trace element composition betweeb marcasite (usually clean) and pyrite (usually containing lots of admixture elements: O, As, Pb, Zn, Cu etc). Lately,  I found in the Kupferschiefer villamaninite CuS2 (pyrite XRD confirmed). As concerns way of origin of framboids there are two mechanism proposed i)bacterial, ii)abiotic. Framboidal pyrite is growing fast in folluted river sediments - probably 2 -3 month, but recent sampling suggests that if polluted river contains appropriate level of nutrients they grow within week and are combined with bacterial films. Cheers, Harry

I am sorry, not familiarized with that. Will follow other suggestions.

Regards, Zenaide

Yes the image looks like Marcasite. The crystal habit of Pyrite is Isometric (cubes) and for Marcasite is dipyramidal, Euhedral (blade or needle shaped) in thin section is the way to identify, as EDS cannot distinguish between Pyrite and Marcasite as both are FeS2 minerals.