Flörkeite |(K3Ca2Na (H2O)12| [Al8Si8O32]
     
Morphology:  
  Short prismatic, pseudo-monoclinic crystals elongated along [100] and somewhat flattened on {010} with a maximum length of 0.6 mm. Additional forms are {100}, {001} and {201}.

brewsteriteFlörkeite, Bellerberg volcano near Ettringen, East Eifel volcanic area, Germany. Width of image 1.2 mm. (© Volker Betz)
Physical properties:
  Cleavage: none. Fracture: irregular.
Hardness:  not determined.
D (calc) = 2.266 gm/cm3.
Luster: vitreous.
Streak: white.
 
Optical properties:
  Color: colorless.
Biaxial (-).  α = 1.506, β = 1.514, γ = 1.518, δ= 0.012, 2Vx  = 70°.
X ˄ c = 43°, Y ˄ b = 40°, Z ˄ b, = 8°
 
Crystallography:
  Unit cell data:
a  19.965, b  14.274, c  8.704 Å , α88.37°, β125.08°, γ  89.57°
Z = 2,  Space group P1 (Lengauer et al. 2009).
     
Name:
  Flörkeite was named by Lengauer et al. (2009) for tiny crystals occurring at Bellerberg volcano near Ettringen, East Eifel volcanic area, Germany. The name honors the mineralogist and crystallographer Otto Wilhelm Flörke, Bochum University, Germany.
     
Crystal structure:
 

The framework of flörkeite is the same as that of phillipsite, consisting of chains of doubly connected 4-rings, linked in the UUDD arrangement, generally known as double crankshaft (dcc in PHI). Like in phillipsite the double crankshaft chains run parallel to the a-axis (see PHI), and result in three sets of channels confined by eight-membered rings of tetrahedra, one parallel to the a-axis (shown in the accompanying figure), one parallel to the b-axis, and another parallel to the c-axis. Because of the framework composition (Si/Al = 1.0), there is strict ordering, not only of the framework but also the channel cations. This ordering distorts the phillipsite framework, resulting in the space group P1 (Lengauer et al. 2009).dachiardite
In the diagram Si-tetrahedra are gray, and Al-tetrahedra are green. In the channels K cations (orange) are bonded to four framework oxygens and two to four H2O molecules (blue) in three different sites; Ca cations (red) are bonded to three oxygens and four or five H2O molecules; and Na cations (yellow) are bonded to two oxygens and four H2O molecules.

     
Occurrence:
  Flörkeite was found in a quarry at the Bellerberg volcano near Ettringen, East Eifel volcanic area, Germany. It occurs in Ca-rich xenoliths, associated with tobermorite, thaumasite, willhendersonite, gismondine, and ellestadite (Lengauer et al. 2009). The alteration of these xenoliths produces minerals typical of low silica environments. All three zeolites, flörkeite, willhendersonite, and gismondine, have framework compositions of Si/Al = 1.0.
     
References:
  Lengauer, C.L., Kolitsch, U., and Tillmanns, E. 2009. Flörkeite, K3Ca2Na[Al8Si8O32]•12H2O, a new phillipsite-type zeolite from the Bellerberg, East Eifel volcanic area, Germany. Eur. J. Mineral., 21, 901-913.