Mineral Mindat link for data

 

Plagioclase series

 

DATA

 

Help!

Plagioclase Feldspar  (Click PPL image to show labels)

Olivine

 

Plagoiclase in a gabbro from Ardnamurchan, Scotland. The plagioclase is layered/aligned and is probably caused by flow rather than settling in this example. Discussion continues. The olivine was the first to solidify, then the plagioclase, the pyroxene last.

 

Width of field of view: 12mm.

 

Hide

lables

NoLable  

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

Olivine XPL view

 

Plagioclase in a gabbro. The plagioclase in this rock is more calcic than normal in a gabbro, and is classified as bytownite. The birefringence is sligltly higher than normal resulting in a yellow tint to come crystals. Albite and carlsbad twinning are visible in the XPL view, and also concentric growth zoning is seen in crystals near extinction.

 

Width of field of view: 12mm.

 

 

   

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

 

 

Olivine rollover

 

Plagioclase in an andesite lava from Montserrat. Phenocrysts of various size and fragments in a glassy matrix. Some show good crystal faces. There are some natural air spaces in this sample, it is very porous.

 

Length of largest crystal: 2.0mm

 

 

Hide

lables

NoLable  

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 


Plagioclase in andesite lava. Well developed oscillatory zoning (see movie clip). Glassy matrix is isotropic and black. Tis type of zoning is common in plagioclase phenocrysts in lavas.

 

Length of largest crystal: 2.0mm

 

 

 

   

Oscillatory

Zoning

Film  

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

 


 

 

Olivine rollover

 

Plagioclase in a granite from Shap. Fairly typical of the appearance of plagioclase in acid rock types. Cloudy alteration, known as sericite or white mica, is so common as to be a useful indicator for plagioclase. This is often in zones with the centre less altered. The alteration can be so intense that it is not possible to otherwise recognise the plagioclase.

 

Width of field of view: 10mm.

 

 

Hide

lables

NoLable  

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 


Plagioclase in a granite. Albite (polysynthetic) twinning is an indicator of plagioclase, quartz shows no twinning, and the alkali feldspars usually only show carlsbad, and also some perthitic exsolution texture.

 

Width of field of view: 10mm.

 

 

 

   

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

 


 

 

Olivine rollover

 

Plagioclase in a dolerite rock, Ardgour, Lochaber. Permian age dyke cutting granite. This section shows two phases of crystallization. Numerous large plagioclase phenocrysts in a fine grained matrix of feldspar laths and augite. Most pale minerals in this section are plagioclase.

 

Width of field of view: 10mm.

 

 

Hide

lables

NoLable  

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 


Plagioclase in a dolerite. Very sharp twinning in both phases.

 

Width of field of view: 10mm.

 

 

 

   

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

 


 

 

Olivine rollover

 

Plagioclase in a basaltic volcanic ejecta block from Stromboli. A matrix of plagioclase laths, some show growth zones of inclusions. Thes are not sericite, but volcanic glass and dust.

 

Width of field of view: 8mm.

 

 

Hide

lables

NoLable  

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 


Plagioclase in a basaltic block. Closely packed plagioclase laths showing excellent twinning and zoning.

 

Width of field of view: 8mm.

 

 

 

   

 

   

Whole slide

View

Zoomit
Mobileicon
 
   Computers
Mobiles

 

 


 

 

All images copyright GEOSEC SLIDES 2013 ~ Please feel free to link to this page ~