The Feldspar-Series
Feldspar consist oft three individual minerals:    
                     Potassium-Feldspar  (Orthoclase and Microcline) 
                     Sodium-Feldspar (Albite and Peristerite) 
                     Calcium-Sodiumnfeldspar (Anorthite) 
These minerals also constitute a isomorphous series in which the minerals are mixed, e.g:  Plagioclase (Sodium and Calcium-Sodium-Feldspärs) 
The hardness of all feldspars is about 6 - 6,5. 

Potassium-Feldspars form two modifications: 
 

    Amazonite (Microcline), has a triclinic chrystal system and forms a green massive  material or even a translucent blueish or greenish aggregate. The name oft this gem also indicates its occurence: Colorado (USA), Brazil, India and Madagascar.
 
    Moonstone (Orthoclase)  chrystallizes monoclinical and forms translucent colourless or yellowish gem material. 
    The beautiful blue schiller (adularescence), that  is characteristical for all moonstones, is due to a peculiarity in the structure, where small layers 

    of orthoclase and albite are arranged. 
    Sources of moonstone: USA, Madagascar, Brazil and India ( yellow moonstone). 

    Orthoclase is a champagne-coloured variety of Madagascar and Burma. 
     

 

Sodium-Feldspars   

     

    Albite(Sodium-Feldspar) also forms moonstones, but it is always mixed with oligoclase. 

    Peristerite is a opaque, brown or white aggregate with a blue shiller. 
    Occurences of  Peristerite: Canada.

 

Calcium-Sodiumfeldspars   
 

    Anorthite  
     
Plagioclase---(Mixture of  Sodium and Calcium-Sodiumfeldspars) 
    Labradorite is a triclinic aggregate, single crystals are very seldom. Labradorite was first found on the semi-island of  Labrador and shows a brillant play of all possible colours which flashes out over large areas of the grey-coloured mineral.This schiller is due to the interference of light on microscopical twin lamellaea.  
    Occurences: Canada, USA, Mexico,  Russia. 
     
     
      

    Aventurine (Oligoclase), also known as Sunstone, forms a triclinic aggregate.  
    Due to small  platy crystals of  Goethite or Hematite the gem material gets a golden or reddish brown colour and specular reflections. 
    Sources of Aventurine: Canada, USA, India, Norway, Russia 

    Andesine is a green, opaque aggregate. 
     
     

    Bytownit ist a reddish or yellowish translucent Feldspar.