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This article contains statements that are disputable.
The metamorphic model of pegmatite formation says that the origin of pegmatite melts are particularly felsic metamorphic rocks. For the Evje-Iveland pegmatite swarm in the south of Norway this seems to be incorrect. According to Snook the melts are derived from mafic rocks: https://ore.exeter.ac.uk/repository/bitstream/handle/10871/14884/SnookB.pdf?sequence=1&isAllowed=y
The speed of crystallisation is another issue. In ELEMENTS Volume 8, Number 4 • August 2012 of the Mineralogical Society of America there was an article where the speed of crystallisation of some Californian pegmatites was presented. My copy of the magazine has disappeared and there is no online copy, so I cannot say on which page this is published. But I recall that it was more a matter of months or years, rather than thousands of years.
Very likely the picture is more complicated. The Evje-Iveland pegmatites formed in a completely different setting than the Californian pegmatites. Here it can be assumed that the bodies of molten rock slowly cooled down while the crust was slowly moving upward. But that in itself does not mean the process of crystallisation therefore also was slow.
I do not want to be involved in editting this article; this is not my field of expertice. I only want to say that a true expert should be encouraged to get involved in improving this article. Even though that is no guarantee for success. I refer to the PEG2017 symposium on Norwegian pegmatites in Norway. The lectures made it clear that there was no consensus on how pegmatites formed. http://geologi.no/images/GeologiskeGuider/PEG2017_Excursion_Guide_NGF_Series_2017-6_red.pdf (just as reference, there is nothing about the discussions in this publication.) Ronald Werner ( talk) 11:25, 25 March 2021 (UTC)
It is very controversial the origin of pegmatites.
After Chris Check "There are many theories about the origin of pegmatites and the amazingly large crystals found in some of them. It is theorized that the pegmatite solidified from a aqueous-silica rich magma. Then the action of the hydrothermal waters on the solidified mass reacted with the present minerals to create new and larger crystals. The other less popular theory is that the hot magma, under intense heat and pressure, experienced a sudden drop in heat or pressure which could cause large scale crystallization."
After Bob Linnen, from the Waterloo University, Canada, "The origin of pegmatite and the explanation of how crystals grow so large are controversial. However, the most widely accepted origin is that the crystals grow from water-rich melts, that are also rich in fluxing elements (elements that lower the melting temperature of silicate minerals) such as boron, fluorine and phosphorous. The high concentrations of these fluxing elements also increases diffusivities in the melt, allowing cations to move more quickly to sites of growing crystals, and this results in the growth of very large crystals. The question of why some pegmatites contain gems whereas others do not is also the subject of debate."
My opinion is that we need to be impartial and to explain the two theories. If choice is necessary I vote for the most popular for us the geologists, that is, the emphasis is put on the hydrothermal liquid and its composition and not on the time of crystallization
Eurico Zimbres
Rio de Janeiro University
School of Geology
15:21, 25 January 2006 (UTC)
I don't understand why this article states that the crystal growth must be incredibly fast to allow the crystals to become so large in a pegmatite. I have always thought that larger crystals necessarily implied weaker supersaturation, caused by a slower cooling of the rock.
In fact, what's really important is the ratio between the nucleation speed and the crystallization speed. If there is a fast nucleation and a slow crystal growth, the crystals will be small. With a slow nucleation and a fast crystallization, they will be large. But we could also see large crystals form by slow crystallization, as far as the nucleation process was even slower. This could be achieved by a slower rate of cooling.
Am I right ? Or did I miss something ?
Pijeth 20:59, 4 May 2007 (UTC)
Pls also mention "chrysoberyl" which is defference of the family of Beryl,and it's containing in to pegmatites.
![]() | This ![]() It is of interest to the following WikiProjects: | ||||||||||||||||||||||||||||||
|
This article contains statements that are disputable.
The metamorphic model of pegmatite formation says that the origin of pegmatite melts are particularly felsic metamorphic rocks. For the Evje-Iveland pegmatite swarm in the south of Norway this seems to be incorrect. According to Snook the melts are derived from mafic rocks: https://ore.exeter.ac.uk/repository/bitstream/handle/10871/14884/SnookB.pdf?sequence=1&isAllowed=y
The speed of crystallisation is another issue. In ELEMENTS Volume 8, Number 4 • August 2012 of the Mineralogical Society of America there was an article where the speed of crystallisation of some Californian pegmatites was presented. My copy of the magazine has disappeared and there is no online copy, so I cannot say on which page this is published. But I recall that it was more a matter of months or years, rather than thousands of years.
Very likely the picture is more complicated. The Evje-Iveland pegmatites formed in a completely different setting than the Californian pegmatites. Here it can be assumed that the bodies of molten rock slowly cooled down while the crust was slowly moving upward. But that in itself does not mean the process of crystallisation therefore also was slow.
I do not want to be involved in editting this article; this is not my field of expertice. I only want to say that a true expert should be encouraged to get involved in improving this article. Even though that is no guarantee for success. I refer to the PEG2017 symposium on Norwegian pegmatites in Norway. The lectures made it clear that there was no consensus on how pegmatites formed. http://geologi.no/images/GeologiskeGuider/PEG2017_Excursion_Guide_NGF_Series_2017-6_red.pdf (just as reference, there is nothing about the discussions in this publication.) Ronald Werner ( talk) 11:25, 25 March 2021 (UTC)
It is very controversial the origin of pegmatites.
After Chris Check "There are many theories about the origin of pegmatites and the amazingly large crystals found in some of them. It is theorized that the pegmatite solidified from a aqueous-silica rich magma. Then the action of the hydrothermal waters on the solidified mass reacted with the present minerals to create new and larger crystals. The other less popular theory is that the hot magma, under intense heat and pressure, experienced a sudden drop in heat or pressure which could cause large scale crystallization."
After Bob Linnen, from the Waterloo University, Canada, "The origin of pegmatite and the explanation of how crystals grow so large are controversial. However, the most widely accepted origin is that the crystals grow from water-rich melts, that are also rich in fluxing elements (elements that lower the melting temperature of silicate minerals) such as boron, fluorine and phosphorous. The high concentrations of these fluxing elements also increases diffusivities in the melt, allowing cations to move more quickly to sites of growing crystals, and this results in the growth of very large crystals. The question of why some pegmatites contain gems whereas others do not is also the subject of debate."
My opinion is that we need to be impartial and to explain the two theories. If choice is necessary I vote for the most popular for us the geologists, that is, the emphasis is put on the hydrothermal liquid and its composition and not on the time of crystallization
Eurico Zimbres
Rio de Janeiro University
School of Geology
15:21, 25 January 2006 (UTC)
I don't understand why this article states that the crystal growth must be incredibly fast to allow the crystals to become so large in a pegmatite. I have always thought that larger crystals necessarily implied weaker supersaturation, caused by a slower cooling of the rock.
In fact, what's really important is the ratio between the nucleation speed and the crystallization speed. If there is a fast nucleation and a slow crystal growth, the crystals will be small. With a slow nucleation and a fast crystallization, they will be large. But we could also see large crystals form by slow crystallization, as far as the nucleation process was even slower. This could be achieved by a slower rate of cooling.
Am I right ? Or did I miss something ?
Pijeth 20:59, 4 May 2007 (UTC)
Pls also mention "chrysoberyl" which is defference of the family of Beryl,and it's containing in to pegmatites.