Graphic granite
A rock subtype
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About Graphic granite
Name:
From the Latin graphus (and Greek graphos) meaning "to write", in allusion to the appearance of script-like characters in the polished rock.
An intergrowth of quartz and feldspar which may appear as runic or cuneiform writing (hence the term), as darker and glassier quartz 'characters' or 'letters' in a groundmass of white feldspar (usually microcline). This is found almost exclusively in granitic pegmatites, and is believed to result from simultaneous growth of the feldspar and quartz under conditions which favored the planar growth of feldspar and the rods of quartz. Note that the quartz 'characters' or rods are usually parallel, at least in patches; these patches are also crystallographically parallel, being for the most part of the same quartz crystal. David London in Pegmatites (2008), page 222, said that "it is clear that the network of quartz stringers is almost entirely interconnected in three dimensions through the feldspar host" and provided an explanation with an accompanying diagram to show how this intergrowth crystallized.
The feldspar of graphic granite is often perthitic as well, which adds interest to the texture.
The feldspar of graphic granite is often perthitic as well, which adds interest to the texture.
Coarse and Fine Graphic Textures: Agnew mine, Custer County, South Dakota (left); Pownal, Maine (right)
Unique Identifiers
Mindat ID:
39400
Long-form identifier:
mindat:1:1:39400:2
Classification of Graphic granite
Granite is in section 3 of the QAPF diagram.
Mineralogy of Graphic granite
Essential minerals - these are minerals that are required within the classification of this rock:
| Feldspar > Alkali Feldspar | A subgroup of the Feldspar Group, poor in calcium, and mostly rich in potassium. |
| Feldspar > Plagioclase | (Na,Ca)[(Si,Al)AlSi2]O8 |
| Silica > Quartz | SiO2 |
Synonyms of Graphic granite
Other Language Names for Graphic granite
German:Schriftgranit
Common Associates
Associations Based on Photo Data:
| 17 photos of Graphic granite associated with Quartz | SiO2 |
| 16 photos of Graphic granite associated with Microcline | K(AlSi3O8) |
| 6 photos of Graphic granite associated with Biotite | K(Fe2+/Mg)2(Al/Fe3+/Mg/Ti)([Si/Al/Fe]2Si2O10)(OH/F)2 |
| 4 photos of Graphic granite associated with Muscovite | KAl2(AlSi3O10)(OH)2 |
| 4 photos of Graphic granite associated with 'Smoky Quartz' | SiO2 |
| 4 photos of Graphic granite associated with Albite | Na(AlSi3O8) |
| 2 photos of Graphic granite associated with 'Amazonite' | K(AlSi3O8) |
| 1 photo of Graphic granite associated with Rutile | TiO2 |
| 1 photo of Graphic granite associated with Monazite-(Ce) | Ce(PO4) |
Internet Links for Graphic granite
mindat.org URL:
https://www.mindat.org/min-39400.html
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References for Graphic granite
Reference List:
Johannsen, Albert (1938) A Descriptive Petrography of the Igneous Rocks Vol. 4 - Part I. The Feldspathoid Rocks. Part II. The Peridotites and Perknites.pp.84-91 - "Runite" as Johannsen called graphic granite
Heritsch, Haymo (1953) Röntgenuntersuchungen an Schriftgraniten. Tschermaks Mineralogische und Petrographische Mitteilungen, 3 (2). 126-141 doi:10.1007/bf01120707
Heritsch, Haymo (1953) Weitere Röntgenuntersuchungen an Schriftgraniten. Tschermaks Mineralogische und Petrographische Mitteilungen, 3 (3). 272-281 doi:10.1007/bf01128222
Simpson, Dale R. (1962) Graphic granite from the Ramona pegmatite district, California. American Mineralogist, 47 (9-10) 1123-1138
Åvesland 04 Uranium Mine, Åvesland, Evje og Hornnes, Agder, Norway