Feldspar is a group of minerals which comprises a number of species with varying degrees of isomorphism. Feldspars are subdivided into two sub group, potassium feldspars (orthoclase, microcline) and plagioclase feldspar.
Of gem interest are orthoclase, microcline and plagioclase (albite, labradorite and oligoclase).
In all species chatoyancy and asterism is due to the presence of parallel, oriented inclusions.
Aluminum silicate of potassium, sodium and calcium. KAlSi3O8. Isomorphous series made up of Albite (Na), Oligoclase, Andesine, Labradorite, Bytownite and Anorthite (Ca) where the two end member are NaAlSi3O8 and CaAl2Si2O8.
Well formed crystals as well as massive or tabular habits. Commonly exhibit lamellar twinning.
Anisotropic, D.R.
Not characteristic
None
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