Paragonite

  Paragonite, also known as Natron-Glimmer, Paragonit or Paragonita, is a mineral, related to muscovite. Its empirical formula is NaAl₂(Si₃Al)O₁₀(OH)₂. A wide solvus separates muscovite from paragonite, such that there is little solid solution along the vector Na⁺K^- and apparent micas of intermediate composition is most commonly a microscopic (or even sub-microscopic) intergroth of two distinct micas, one rich in K, and the other in Na. Paragonite is a common mineral in rocks metamorphosed under blueschist facies conditions along with other sodic minerals such as albite, jadeite and glaucophane.