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GeneralThree-pointed stars included

6th Nov 2018 05:48 UTCAndrea Oppicelli

06026590016047025548674.jpg
Hi everyone.

These three-pointed star-shaped images are present as included in a phlogopite sample found in Ariccia (Rome-Italy): what can they be due to? Fov 3 mm.

6th Nov 2018 06:09 UTCPavel Kartashov Manager

Rutile?

12th Nov 2018 07:25 UTCAndrea Oppicelli

Thanks Pavel for the reply. No one else has any ideas?

12th Nov 2018 13:52 UTCKevin Conroy Manager

I was wondering if the iridescent look is from crystals, or could it be that the shapes are hollow spaces in the phlogopite and the color is formed by refracting light?

12th Nov 2018 15:57 UTCKevin Hean

Hi Kevin

I think it is a microscopic gap or space between the Rutile and the Phlogopite that is refracting the light causing the iridescence,

I say microscopic because it appears blue ?

12th Nov 2018 20:46 UTCKevin Conroy Manager

I wonder if all of the shapes that we can see are voids, or if they are crystals. It's hard to tell from the photo but are the stars in a flat plane, or are they curved? It kind of reminds me of molecular models in a chemistry class.

12th Nov 2018 22:08 UTCEd Clopton 🌟 Expert

My first thought was empty channels, too, perhaps from some weird corrosion process following lines of weakness or stress in the pholgopite? If there are solids in the three-pointed stars, there is as Kevin Hean says, air between them and the pholgopite.

13th Nov 2018 05:33 UTCAndrea Oppicelli

07592810016047025551309.jpg
Thank you all for your contribution; some hypothesis seems to be closer to the truth in what you have said.

These particular star images are just some air-filled channels between the phlogopite laminations. The different coloration I think is due to the angle of the light source.

But the star shape?

If the crystal of phlogopite has a hexagonal shape and we put many close together, we obtain a sort of honeycomb shape. The sides between 3 close crystals have just the shape of a 3-pointed star. Here is my simple hand-made drawing the explanation of this phenomenon. The growth of the individual crystals in the three phases and the subsequent delamination between the crystals with penetration of air formed these channels. Just with that shape due to the stepped division between the various crystalline laminae.

 
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