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Collection of Dontgogreen
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dontgogreen




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PostPosted: Dec 15, 2017 08:59    Post subject: Re: Collection of Dontgogreen  

After spending a little time collecting worldwide minerals without any focus, I have narrowed my interest to rutile crystals. I think their beauty is a bit more subtle than many species, and they are generally far more affordable. Here are two Brazilian specimens that I like quite a bit.


golconda5_1.jpg
 Mineral: Rutile (variety struverite)
 Locality:
Golconda pegmatite, Governador Valadares, Vale do Rio Doce, Minas Gerais, Brazil
 Dimensions: ~4.5 cm
 Description:
 Viewed:  618 Time(s)

golconda5_1.jpg



capao de lana_bedogne_ 5pt5cm_2.jpg
 Mineral: Rutile
 Dimensions: 5.5 cm
 Description:
 Viewed:  620 Time(s)

capao de lana_bedogne_ 5pt5cm_2.jpg


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dontgogreen




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PostPosted: Dec 22, 2017 09:26    Post subject: Re: Collection of Dontgogreen  

Hematite and rutile both posses a hexagonal close-packed oxygen sublattice, which enables simple transitions among them by exsolution, epitaxy, and intergrowth (Daneu et al. [2014] and references therein).

Other examples of hematite and rutile intergrowth are the speicmens from Novo Horizonte, Brazil, and those of Mwinilunga, Zambia. A study of the Zambian material indicates that the source of Ti for rutile growth is the hematite crystal itself. Diffusion of Ti ions lead to topotaxial nucleation and growth of rutile on structurally compatible lattice planes (Rečnik et al., 2015). I am not sure whether or not this also holds true for specimens from Cavradi, as I have not been able to find a similar study. If anyone is aware of one, please direct me to it. Additionally, if you have Mwinilunga specimens, I would gladly trade for them!



cavradi1.jpeg
 Mineral: Hematite with Rutile
 Locality:
Cavradi, Curnera Valley, Tujetsch (Tavetsch), Vorderrhein Valley, Grischun (Grisons; Graubünden), Switzerland
 Dimensions: ~4 cm
 Description:
 Viewed:  502 Time(s)

cavradi1.jpeg


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Philippe Durand




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PostPosted: Dec 22, 2017 10:23    Post subject: Re: Collection of Dontgogreen  

Ha ! I love this hematite; my favorite mineral.
It is a marvelous specimen.
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Tobi




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PostPosted: Dec 22, 2017 13:35    Post subject: Re: Collection of Dontgogreen  

dontgogreen wrote:
Hematite with rutile
Cavradi, Curnera Valley, Tujetsch (Tavetsch), Vorderrhein Valley, Grischun (Grisons; Graubünden), Switzerland
~4 cm!
Great Cavradi specimen!!!
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Jordi Fabre
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PostPosted: Dec 23, 2017 16:52    Post subject: Re: Collection of Dontgogreen  

dontgogreen wrote:
...A study of the Zambian material indicates that the source of Ti for rutile growth is the hematite crystal itself. Diffusion of Ti ions lead to topotaxial nucleation and growth of rutile on structurally compatible lattice planes (Rečnik et al., 2015)...

Before the text mentioned it was this note related with the first analysis of the Zambian material wrote in December 2007 by the late Dr. Joan Viñals :

Comments on the possible pseudomorph of rutile and hematite from ilmenite crystals:

Commonly, rutile occurs as oriented crystals on hematite crystals. This may be due as an epitactic growth or from an exsolution process. In both cases, hematite appears as single crystals or as aggregates of a limited number of single crystals. Microscopic examination of material from Jordi Fabre shows that rutile forms a delicate intergrowth of rutile and hematite. However, hematite occurs as very fine grained masses which form the interstices between the rutile needles. This could be consistent with an hydrothermal (oxidizing) alteration process of a former ilmenite crystals. Textures of this type were reported by Ramdohr (The ore minerals and their intergrowths. Pergamon Press, Oxford.1980. Vol 2. p.1008). In this case, rutile forms trigonal network in the basal sections of the former ilmenite, while fine grained hematite filled the interstices.



Hematite and Rutile - Mwinilunga_Zambia.jpg
 Description:
The original analysis and report written by the missed Dr. Joan Viñals
 Viewed:  370 Time(s)

Hematite and Rutile - Mwinilunga_Zambia.jpg


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dontgogreen




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PostPosted: Jan 12, 2018 23:38    Post subject: Re: Collection of Dontgogreen  

The hoppered termination lets the red color come through nicely at the top. These striated prisms are some of my favorites.


hiddenite_melanson_1.jpg
 Mineral: Rutile
 Locality:
Hiddenite, Alexander County, North Carolina, USA
 Dimensions: 2.7 cm
 Description:
 Viewed:  188 Time(s)

hiddenite_melanson_1.jpg



hiddenite_melanson_2.jpg
 Mineral: Rutile
 Locality:
Hiddenite, Alexander County, North Carolina, USA
 Dimensions: 2.7 cm
 Description:
 Viewed:  184 Time(s)

hiddenite_melanson_2.jpg


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dontgogreen




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PostPosted: Jan 13, 2018 23:28    Post subject: Re: Collection of Dontgogreen  

A multiply twinned equant crystal from Graves Mountain with excellent luster.


graves mtn cyclic thumbnail.jpg
 Mineral: Rutile
 Locality:
Graves Mountain, Lincoln County, Georgia, USA
 Dimensions: 2.5 cm
 Description:
 Viewed:  102 Time(s)

graves mtn cyclic thumbnail.jpg


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