metamorphic

rocks

 

minerals

 

 

A felsic igneous rock from the bottom of Bowen's Reaction Series. Typically light colored (few mafic minerals) with orthoclase the most obvious mineral (typically pink but also white or greenish), but quartz >20% is essential.
     

This rock can be confused with a syenite which appears superficially similar. The amount of quartz is the key: <20% and the rock is "quartz syenite".

 

Typical Minerals
quartz > 20% 
orthoclase is greater than 
Plagioclase
Mafics - < 10%

 

granite, as with all felsic rocks, is found on continents.  It is one of the last fractionation products and typically results from partial melting of the lower crust.

 

 

 

In this detail the pinkish colored orthoclase stands out clearly, but quartz is also common (clear, glassy, no cleavage; for example the grain on the bo

ttom, just left of center.) 

 

  

 

 

A felsic igneous rock from the bottom of Bowen's Reaction Series. Typically light colored (few mafic minerals) with sodium plagioclase the most obvious mineral, but quartz >20% is essential. orthoclase can be present in plagiogranite, but here there is virtually none. muscovite it not common in most igneous rocks but this specimen has some; it appears brassy and shiny.
     

This rock can be confused with a monzonite which appears superficially similar. The amount of quartz is the key: <20% and the rock is "quartz monzonite". Watch the mafics, however; if they exceed 5-10% then the rock is heading toward a diorite or granodiorite.

 

muscovite - trace (brassy looking)

 

Plagio-granite, is the result of fractional melting above a rapid subduction zone. It is commonly produced in volcanic arcs, and in cordilleran mountain building (subduction along the edge of a continent, such as with the Andes Mountains). Plagio-granite is a common component of the cores (Cratons) of continents, especially the most ancient portions which were constructed from numerous small volcanic arcs with rapid subductions in the earth's earliest, hottest phases. Another common name for Plagio-granite is tonolite.

 

 

 

In this detail the plagioclase stands out clearly.

 

The quartz is harder to see in the photo, but are clear grains, grayish not white, scattered among the plagioclase crystals. Mafics are few but consist of biotite crystals. There is also muscovite (or this muscovite in an alkali granite) in this specimen but it just does not show up in the photograph; you must rotate the crystal in the light under a microscope for it to show up.