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Mike Wood
Joined: 16 Dec 2010
Posts: 456
Location: Northern England
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 Posted: Jan 14, 2015 18:38 Post subject: Re: Oddities from Brandberg, Namibia |
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Incredibly clear and sharp photo's of the quartz Pierre!
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Fiebre Verde
Joined: 11 Sep 2013
Posts: 944
Location: Paris Area
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| Posted: Jan 14, 2015 19:19 Post subject: Re: Oddities from Brandberg, Namibia |
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| Excellent photos Pierre!
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Duncan Miller
Joined: 25 Apr 2009
Posts: 138
Location: South Africa
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| Posted: Jan 15, 2015 04:22 Post subject: Re: Oddities from Brandberg, Namibia |
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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
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vic rzonca
Joined: 18 Nov 2008
Posts: 820
Location: MA
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| Posted: Jan 15, 2015 07:10 Post subject: Re: Oddities from Brandberg, Namibia |
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| 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?
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 15, 2015 11:25 Post subject: Re: Oddities from Brandberg, Namibia |
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| xenolithos wrote: | 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 |
Hi Duncan, I held the crystal and felt nothing negative, only positive energy! Only kidding! :-)
I looked up in the dictionary, inverted - 'put upside down or in the opposite position, order, or arrangement'. Just a question, why would some sections of the interior crystal form after the main crystal? I have seen water and air bubbles in some of these, clearly indicating that some, or all, are hollow. When you view broken crystals, the formations can be clearly seen. My guess is that these negative/inverted crystals form as a result of gas(H) trapped inside and that these form together with the main crystal.
Anyway, that is just my thought. Regards.
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Pierre Joubert
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 15, 2015 11:43 Post subject: Re: Oddities from Brandberg, Namibia |
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| vic rzonca wrote: | | 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 ? |
Hi Vic. Looking at your specimens, it seems to me that the conditions under which they formed are fairly similar to that of the Brandberg area. I am sorry, I cannot answer your question.
How about a photo or two of some of your specimens with inverted crystals? Regards.
| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia |  |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. This crystal features in our collection. It has a story to it. In short, I gave this crystal to Riana not long after we met. |
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| Viewed: |
26751 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26752 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26787 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26759 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26758 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26759 Time(s) |
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| Mineral: | Quartz |
| Locality: | | Brandberg area, Erongo Region, Namibia | |
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| Dimensions: | 33 x 13 x 12 mm |
| Description: |
| Quartz with inverted crystals. Same as above. |
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| Viewed: |
26794 Time(s) |
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Pierre Joubert
'The tree of silence bears the fruit of peace. ' |
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 15, 2015 11:59 Post subject: Re: Oddities from Brandberg, Namibia |
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I apologize, I missed the comments of Michael, Don, Mike and Gerard. Thank you very much! Regards.
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Pierre Joubert
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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| Posted: Jan 15, 2015 13:52 Post subject: Re: Oddities from Brandberg, Namibia |
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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...
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 15, 2015 14:09 Post subject: Re: Oddities from Brandberg, Namibia |
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| Josele wrote: | 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... |
Hi Josele. Thank you for your kind compliments. I do not mind if you use one or more of the photos to draw crystallographic diagrams to illustrate your point. I am afraid my knowledge here is insufficient. Best regards.
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Pierre Joubert
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Josele
Joined: 10 Apr 2012
Posts: 410
Location: Tarifa, Spain
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| Posted: Jan 15, 2015 15:04 Post subject: Re: Oddities from Brandberg, Namibia |
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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.
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Martin Rich
Joined: 15 Aug 2013
Posts: 127
Location: Lower Austria
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| Posted: Jan 16, 2015 00:11 Post subject: Re: Oddities from Brandberg, Namibia |
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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
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 16, 2015 03:56 Post subject: Re: Oddities from Brandberg, Namibia |
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| Martin Rich wrote: | Hello Pierre!
Excellent photos and the negative crystals are textbook examples! It seems that quartz shows such formations more frequently as other minerals, but this also known from fluorite, calcite, galenite (!), gypsum and others. I think it is not really clear what reasons are accountable for this 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 |
Hi Martin. Thank you for the compliment. I spent a few hours photographing these 2 specimens and discarded a few hundred photos! Maybe one day I will have a focus rail and a SLR camera with a Tamron lens:-) The growing conditions of the Brandberg quartz crystals were very harsh, so I can imagine that the crystals grew quickly. Any more info will be welcome. Regards.
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Pierre Joubert
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James Catmur
Site Admin
Joined: 14 Sep 2006
Posts: 1479
Location: Cambridge
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| Posted: Jan 16, 2015 07:22 Post subject: Re: Oddities from Brandberg, Namibia |
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Pierre
Great photos and it is great to see the negative crystals so clearly.
Thank you
James
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Pierre Joubert
Joined: 09 Mar 2012
Posts: 1605
Location: Western Cape
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| Posted: Jan 16, 2015 09:01 Post subject: Re: Oddities from Brandberg, Namibia |
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| James wrote: | Pierre
Great photos and it is great to see the negative crystals so clearly.
Thank you
James |
Thank you James! I would love to have Peter's opinion on this. Regards.
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Pierre Joubert
'The tree of silence bears the fruit of peace. ' |
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cascaillou
Joined: 27 Nov 2011
Posts: 263
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| Posted: Jan 22, 2015 04:17 Post subject: Re: Oddities from Brandberg, Namibia |
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| 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)
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