Direnzoite |NaK6MgCa2(H2O)36| [Al13Si47O120]
  Hemispheres of acicular crystals, up to 0.5 mm.
Physical properties:  
  Cleavage:  [010] distinct.
Hardness:  4.5.  D (meas) = 2.12 gm/cm3.
Luster: vitreous to silky. Streak: white.
Optical properties:            
  Color: Colorless. Average refractive index: 1.483.  
  Unit cell: a 7.5789,  b 18.201,  c 26.1539 Å.
Space group: Pmmn.  Z = 1. (Galli and Gualtieri, 2008)
  Direnzoite was described and named by for a mineral found in a xenolith collected at Mont Peylenc, near the town of St. Pierre Eynac, in the volcanic province of Velay, France. The name honors Dr. Francesco Di Renzo,  Research Director at the Laboratoire de Matériaux Catalytiques et Catalyse en Chimie Organique, Ecole Nationale Supérieure de Chimie de Montpellier (France).
Crystal structure:  
  The framework of direnzoite and the isotypic synthetic ECR-1 (Leonowicz and Vaughan, 1987, Chen et al. 1996, Gualtieri et al. 2006, and Galli and Gualtieri 2008) consist of layers of mordenite and mazzite connected in a regular 1:1 stacking sequence (see figure and EON).
Six non-framework sites and 14 distinct sites for the H2O molecules were determined in direnzoite (Galli and Gualtieri 2008). Three sites are occupied by K ions with Na, Ca, and Mg distributed over three other distinct sites. All the non-framework sites display partial occupancy. K1 was refined at the origin, inside the 8-ring channels of the mazzite sheet with eightfold coordination with 6 framework oxygens and 2 H2O molecules. K2 is located within the large 12-ring channel of the mordenite sheet at the window formed by the eight-membered ring with ninefold coordination with 6 framework O atoms and 3 H2O molecules. K3 is found within the 12-ring channel close to the bottom 6-membered ring. It has eightfold coordination environment with 4 oxygens and 2 H2O molecules. Calcium also in the 12-ring channel has a distorted pyramid-like, fivefold coordination with H2O molecules. Sodium is in the 8-ring channels of the mordenite sheet with fourfold coordination environment with one framework oxygen and 3 H2O. Like in mazzite, Mg is at the center of the gmelinite cage, totally surrounded by H2O molecules.

Chemical composition:
  Direnzoite was found in a glassy, feldspathic xenolith hosted by porphyritic basalt at Mont Peylenc, near the town of St. Pierre Eynac, in the volcanic province of Velay, France. The cavi­ties are filled with newly formed minerals grown on the clayey substrate. Direnzoite grew in cavities with other zeolites (mordenite, phillipsite, merlinoite, erionite, analcime, and chabazite) in ad­dition to calcite and aragonite, all resulting from late stage alteration of the host rocks.
  Leonowicz, M.E. and Vaughan, D.E.W. 1987.  Proposed synthetic zeolite ECR-1 structure gives a new zeolite framework topology. Nature, 329, 819-821.

Chen, C.S.H., Schlenker, J.L. and Wentzek, S.E. 1996. Synthesis and characterization of synthetic zeolite ECR-1, Zeolites, 17, 393-400.

Gualtieri, A.F., Ferrari, S., Galli, E., Di Renzo, F. and van Beek, W. 2006. Rietveld structure refinement of zeolite ECR-1. Chem. Mater., 18, 76-84.

Galli, E. and Gualtieri, A.F. 2008. Direnzoite, a new zeolite from the Massif Central (France): Description and crystal structure.  Am. Mineral. 93, 95-102.