It is difficult to say anything based solely on these photographs. To determine such a sample, I can recommend using a UV flashlight (lamp) or 405 nm laser; diamonds most often luminesce, while quartz does not have luminescence.

Chemical analysis will identify this material.

DEAR MIKHAIL AND RAJAMOHAN THANK YOU FOR YOUR ANSWERS. I WAS WONDERING IF THE CRYSTAL CAN BE IDENTIFIED ONLY BY THE DIGITAL STEREOSCOPIC MICROSCOPE.

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IOANNIS

I HAVE ADDED 3 PHOTOS FROM A NEW 2MM CRYSTAL BECAUSE I LOST THE PREVIOUS ONE. THE CRYSTAL SEEMS TO HAVE AN ADAMANTINE TO SUBADAMANTINE (FROSTED?) LUSTRE EVEN UNDER NATURAL LIGHT. IS THIS A DIAMOND?

IOANNIS

All that glittering is not gold. Please check by chemical analysis.

I WILL, IN TIME RAJAMOHAN, CHECK IN THE RAMAN. BEFORE THAT I COULD CHECK IT WITH A UV FLASHLIGHT, ALTHOUGH THIS METHOD ONLY WORKS FOR 85% OF C-DIAMONDS.

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IOANNIS

Have you tried a hardness test? If it can scratch corundum (ruby, sapphire) or WC (tungsten carbide) then it is most likely diamond.

THANK YOU FOR YOUR INTERESTING ANSWER INGRID AND MERRY CHRISTMAS.

IOANNIS

I HAVE ATTACHED TWO BETTER (CLEARER) PHOTOS INSTEAD OF THE TWO LAST ONES. THE ADAMANTINE LUSTRE HERE IS QUITE OBVIOUS.

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IOANNIS

HERE IS ANOTHER PHOTO WITH A WHITE BACKGROUND UNDER NATURAL LIGHT (LIKE THE FIRST PHOTO). YOU CAN SEE THE ADAMANTINE LUSTRE.

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IOANNIS

The fastest and best preliminary test works based on the large hardness of the diamond. I therefore agree with Ingrid Kjasgaard's answer. Since your stones are 2 mm in size, you can just about hold them between 2 fingers.

Use a quartz crystal with a bare clean surface, for example a citrine crystal. Now try to scratch its surface with the small “diamond”. If you succeed easily scratching the quartz surface, then your stone could be a diamond (or at least a corundum). If you don't succeed, or only with great force and only a few scratches appear, then you probably have a quartz.

If you just choose between quartz and diamond, according to the picture, it is indeed closer to diamond. However, the picture does not show the luster very well, nor does it show the topography details very well. It is recommended to zoom in on the surface to see if there are regular equilateral triangle bumps or pits, if there are, then diamonds are more likely. Of course, if you do a Raman or FTIR test, you can basically get a definitive conclusion.

DEAR JOHANNES

GOOD MORNING AND THANK YOU FOR YOUR REPLY. THE CRYSTAL IS ONLY ONE BUT PHOTOS LOOK DIFFERENT UNDER NATURAL LIGHT (CLOUDY DAY) AND SPOTLIGHT AND DIFFERENT BACKGROUND. I AGREE WITH YOU THAT THE BEST (EASIEST) CHARACTERISTIC TO TEST IN DIAMONDS, AFTER LUSTRE, IS HARDNESS. THAT IS WHAT THE VISITORS-PROSPECTORS IN THE CRATER OF DIAMONDS STATE PARK IN ARKANSAS (USA) DO. HOWEVER, AS I MENTIONED BEFORE, IF THERE ARE MINOR CRACKS IN THE DIAMOND, IT MAY FALL APART DURING THE HARDNESS TEST (I WOULDN'T WANT THAT).

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IOANNIS

DEAR B.J.

GOOD AFTERNOON AND THANK YOU FOR THE REPLY. I KNOW THAT THE PHOTOS ARE NOT THE BEST POSSIBLE. I WILL TRY TO ADD TO THE QUESTION BETTER PHOTOS WITHIN THE WEEK. NOTE THAT NOT ALL DIAMONDS HAVE SMALL TRIAGLES IN THE SURFACE (E.G. IRREGULAR DIAMONDS). ALSO, WHEN INSPECTING THE CRYSTAL I NOTICED A VERY SMALL PURPLE CRYSTAL ON THE SURFACE. I THINK IT IS GARNET. DIAMONDS AND GARNETS ARE COGENETIC IN THE LITHOSPHERIC MANTLE. I THINK RAMAN WHICH IS NON-DESTRUCTIVE WOULD DO THE JOB.

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IOANNIS

DEAR COLLEAGUES

I HAVE NOW CHECKED THE CRYSTAL WITH THE ADAMANTINE LUSTRE WITH A CERTIFIED GEMMOLOGIST IN A STATE OF THE ART RAMAN (GemmoRaman-532SG). THE CRYSTAL IS NEITHER QUARTZ NOR DIAMOND. IT HAS 2 PEAKS, ONE MAJOR AT 475 AND ONE MINOR AT 224 (SEE ATTACHED PDF). I CHECKED THE RRUFF RAMAN DATABASE AND IT DOESN'T COMPLY WITH ANY KNOWN MINERAL. WHAT IS IT? PLEASE COMMENT.

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IOANNIS

Ioannis Kamvisis This Raman spectrum is similar to sulfur peaks.

Article Nanostructure of matrices for sulfur constructional composit...

DEAR MIKHAIL

THANK YOU FOR YOUR INTEREST. THE CRYSTAL HAS ONLY 2 RAMAN PEAKS WHILE SULPHUR HAS MORE. THE MAJOR PEAK OF THE CRYSTAL IS AT 475 AND THE MINOR AT 224. IN SULPHUR IT'S VICE VERSA.

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IOANNIS

Ioannis Kamvisis The ratio of peaks of sulfur compounds may vary, for example https://www.sciencedirect.com/science/article/abs/pii/S0009254101003023. And other peaks are not visible due to the low resolution of the spectrum.

DEAR MIKHAIL

THE RRUFF MINERAL DATABASE, WHICH CONTAINS MORE THAN 5100 MINERALS, DID NOT IDENTIFY THIS CRYSTAL AS SULPHUR. IN ADDITION, TWO EXPERT GEOLOGISTS IN RAMAN, TO WHICH I SENT THE DIAGRAM, ALSO COULDN'T IDENTIFY THIS MINERAL. FINALLY, NOTE THAT SULPHUR IS YELLOW WITH A RESINOUS OR GREASY LUSTRE WHILE THE CRYSTAL IS GREYISH WITH AN ADAMANTINE LUSTRE.

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IOANNIS

I don't know what the connection is between the presented Raman spectrum and the crystal. Perhaps the spectrum of the film on the surface, or inclusions in the crystal was obtained. But with 95% probability this is a spectrum of sulfur, including the RRUFF database, the spectrum is presented on the BROAD SCAN WITH SPECTRAL ARTIFACTS tab https://rruff.info/sulfur/R040135

Article Remote Raman Detection of Chemicals from 1752 m During After...

THANK YOU FOR YOUR INTERESTING ANSWER. I ACTUALLY DID 2 XRD ANALYSES THAT SHOWED TO BE A NEW VARIETY OF QUARTZ WITH ADAMANTINE LUSTRE WHICH CONTAINS MINOR Al2O3, K2O AND TiO2.

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IOANNIS