Feldspar Visible Spectra (generally 350 - 2500 nm)


Pale yellow color in feldspar is due to Fe3+ in the tetrahderal Si/Al site. This color is often masked by the pervasive turbidity of common feldspars. Smoky color, the result of radiation damage from the decay of potassium-40, is also common but often masked.

Blue color in the amazonite variety of potassium feldspar (and pale-blue albite as well) is from the interaction of trace amounts of Pb2+ in the feldspar with ionizing radiation (again, the radiation usually comes from the decay of potassium-40). Water molecules also must be present in the structure for the coloration to occur. Lead-containing feldspars with a higher degree of Al/Si disorder (typically orthoclase) are green where more the more common ordered feldspars (microcline) become blue from irradiation. Feldspars with intermediate ordering often show both a green and a blue component in the spectrum.

Pale blue color also occurs in plagioclase and occasionally, intense blue color can be found as in the sample from the Behive #1 mine in the Boulder Batholith, MT. Instances can even be found when colorless microcline can be found in contact with pale blue albite such as the material from the White Queen Mine, Pala, CA

There are varieties of plagioclase feldspar colored green and red from copper ions and colloidal copper found in southwestern Oregon.. 


Yellow, iron-containing feldspar

Blue to green, lead-containing potassium feldspar (amazonite variety)


Blue, lead-containing plagioclase feldspars


Grey feldspar (smoky variety)  

Red and green, copper-containing feldspar (sunstone variety)

   

Pink albite

 

Link to a collection of references to mostly color and visible spectroscopy of feldspars


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revised 5-Jul-2022