Parallel, millimeter-thin layers of mineral that occur perpendicular to the "b" crystallographic axis form a type of twinning named for one mineral of this class that also exhibits twinning via the Manebach, Baveno, and Carlsbad laws. At the low anorthite end of a series, Albite is a transition between two classes of this mineral. Minerals of this type with only Potassium or Sodium as metals are known as the alkali class of these tectosilicate minerals whose other major class forms the continuous branch of the Bowen's reaction series. The Calcium rich Plagioclase and the Potassium rich Orthocl
Parallel, millimeter-thin layers of mineral that occur perpendicular to the "b" crystallographic axis form a type of twinning named for one mineral of this class that also exhibits twinning via the Manebach, Baveno, and Carlsbad laws. At the low anorthite end of a series, Albite is a transition between two classes of this mineral. Minerals of this type with only Potassium or Sodium as metals are known as the alkali class of these tectosilicate minerals whose other major class forms the continuous branch of the Bowen's reaction series. The Calcium rich Plagioclase and the Potassium rich Orthoclase are the most observed members of, for 10 points, which mineral class which is a 6 on the Mohs scale of hardness and whose name comes from the German for Field Rock.
Parallel, millimeter-thin layers of mineral that occur perpendicular to the "b" crystallographic axis form a type of twinning named for one mineral of this class that also exhibits twinning via the Manebach, Baveno, and Carlsbad laws.
feldspars [accept twinning before mention]