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PhotosPOTD 14 Jan 2024: W = "wow!" + "what the heck?"

14th Jan 2024 07:51 UTCDon Windeler

Cronstedtite, Siderite

Brunita open pit (Brunita Quarry), La Unión, Murcia, Spain

So I found myself just staring at this photo, thinking how cool it is, then wondering "which is cronstedtite and which is siderite?" So I opened up the main photo and description.

If I'm interpreting right, all the black stuff is the cronstedtite and the siderite is limited to the brown in the upper right. My "what the heck?" is thus wondering what is going on in the middle of the photo. If that's all cronstedtite, how do you get those sharp tetrahedral (I think) crystals next to the round discs? Especially since they look intergrown to the extent you'd think they were coeval?

Beautiful pic that warrants more desciption, or at least thoughtful bloviating. ;)

Cheers,

14th Jan 2024 08:59 UTCEddy Vervloet Manager

I was wondering exactly the same thing, Don!

Great minds think alike and all that... :)

14th Jan 2024 09:22 UTCElmar Lackner Expert

I think this is a matter of intergrowth twinning and/or polytypism. This goes far behond my knowing of crystallography :-). But this wonder of nature is one of the reasons to collect Minerals.

Best regards

Elmar

14th Jan 2024 09:51 UTCHerwig Pelckmans

Yeah, cronstedtite certainly is a cool mineral (and for many reasons one of my favorites).

All the black is indeed cronstedtite. It does come in different habits. Sometimes only the "rounded discs", and sometimes only the trigonal pyramids, and sometimes both, like in this photo.

Elmar, thank you once more for this (and the many other) excellent photos you contribute to mindat!

15th Jan 2024 12:08 UTCUwe Kolitsch Manager

It does come in different habits.

The two habits are almost certainly due to different polytypes.

14th Jan 2024 12:31 UTCEd Clopton 🌟 Expert

It would be helpful to edit the caption to indicate that the photo shows cronstedtite in two different habits, sharp tetrahedral crystals and smaller discoidal crystals, both black, and that the siderite is the brown mineral at upper right. That would reduce the uncertainty of a viewer (like me) who isn't familiar with the ins and outs of cronstedite.

14th Jan 2024 19:30 UTCElmar Lackner Expert

Done ;-)

14th Jan 2024 20:56 UTCRalph S Bottrill 🌟 Manager

Remarkable!

15th Jan 2024 13:45 UTCRolf Luetcke Expert

From a friend who lives near the location, the mine has long been flooded and is fenced, so nothing like this will ever be found again, great specimen and photo.

15th Jan 2024 14:23 UTCBret Howard 🌟

Something that makes this specimen even more interesting is that the disks appear to form as the termination of a "stem" that seems to be comprised of parallel growths of crystals.

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