FMF - Friends of Minerals Forum, discussion and message board

[Mike Wood]

Incredibly clear and sharp photo's of the quartz Pierre!

[Fiebre Verde]

Excellent photos Pierre!

[Duncan Miller]

Hello Pierre

Don't you mean 'negative crystals', rather than 'inverted crystals'? I think they form as the trapped solution cools and the dissolved silica crystallises on the inner walls of the host quartz, necessarily following the crystallographic structure and orienation of the host. The gas bubble forms as the gas too comes out of solution. Gentle heating can cause the gas to redissolve.

Duncan

[vic rzonca]

Likewise, Pierre, I have usually termed them negative crystal inclusions, but I suppose inverted works, although when I think of inverted it is as up-side-down, not out-side-in. It amazes me that these inclusions match perfectly the exterior geometry of the host crystal, but surely makes sense. It seems the Brandberg quartz is rich in very interesting inclusions. Am I wrong, or does quartz exhibit these negative - invert crystal forms more offen than most minerals?

[Pierre Joubert]

[Pierre Joubert]

[Pierre Joubert]

I apologize, I missed the comments of Michael, Don, Mike and Gerard. Thank you very much! Regards.

[Josele]

Fascinating quartz and photos! Congratulations!
Probably I'm confused:
- Crystallographic orientations of host and negative crystals seem be different.
- In some photos seems as there is a 60º crossed striation, not usual on quartz.
Don't got it...

[Pierre Joubert]

[Josele]

Pierre, also mine is insufficient. Maybe someone can help on this.
Negative crystal seem be tabular. Biggest faces seem be of the prism but I'm not sure. Perhaps they are r or z faces and that would explain the apparent different orientation.
That's all I can talk about.

[Martin Rich]

Hello Pierre!

Excellent photos and the negative crystals are textbook examples! It seems that quartz shows such formations more frequently than other minerals, but this is also known from fluorite, calcite, galena (!), gypsum and others. I think it is not really clear what reasons are accountable for these negative crystals. One reason is, that crystals are grown fast and I think the temperature is also a reason, but I'm not sure - if I have some time, I will look in my library.

Martin

[Pierre Joubert]

[James Catmur]

Pierre

Great photos and it is great to see the negative crystals so clearly.

Thank you

James

[Pierre Joubert]

[cascaillou]

The crystallographic orientation of a negative crystal is the same as the host crystal. The only difference that is seen in your pictures being the unequal development of facets (but each facet of the negative crystal remains strictly parallel to the host crystal facets)

[Tiffany7mo]

Whoa, that's cool. Excellent photos!

[Pierre Joubert]

[Pierre Joubert]

Fake specimens (or doctored specimens) are a rarity from Brandberg, so I consider them as 'oddities'.
A while ago, we purchased some mineral specimens from a friend. When he showed us some matrix amethyst crystal specimens, he said that he thought that they may have been glued onto the matrix. We purchased them anyway and later on I studied them carefully. I found 4 that have been glued on basalt matrix and covered expertly with very small calcite crystals. The only 'give away' was an unusual sheen on the calcite, suggesting glue. Whoever did this, knows his job. I placed 2 of the specimens in pool acid which removed the crystals from their matrix. The calcite dissolved leaving only a lump of, what looks like epoxy. I am keeping the 2 remaining specimens intact as rare samples of 'doctored' Brandberg specimens. Meanwhile, we are working to trace the culprit/s and will warn them to discontinue their trade or we will report them to the Namibian mine authorities.

[Pierre Joubert]

The first two fake specimens that was exposed in the acid bath. I must stress that 'doctored' specimens from Namibia, and especially from Brandberg area, are rare. These are the fiirst we have ever encountered.

[Mike Wood]

Beautiful amythest crystals Pierre, shame about the glue. I must say your photo's are extremely clear and well composed. Thanks for taking the trouble to photograph and post these glued specimens.

Best regards,
Mike