Roggianite |Ca2 (H2O)2.5| [BeAl2Si4O13(OH)2]
       
Morphology:    
  Tetragonal acicular crystals up to 0.02 mm thick and 10 mm long, commonly in radiating and spherulitic clusters.
   
Physical properties:  
  Cleavage: {110} perfect.
Hardness:  not determined.
D = 2.02 (meas) 2.63 (calc) gm/cm3.
Luster: vitreous.
Streak: white.
 
   
Optical properties:            
  Color: pale yellow.
Uniaxial (+).  ω  1.527,  ε  1.535
 
   
Crystallography:  
  Unit cell data:
a  18.33   c  9.16 Å,  Z = 8, Space group  I 4/mcm
 
   
   
       
Name:  
  Roggianite was described and named by Passaglia (1969) to honor Aldo G. Roggiani, Italian teacher of natural sciences, who first found the mineral. The type locality is an albitite dike at Alpe Rosso in Val Vigezzo about 1.5 km south of Orcesco, Novara Province, Italy. The same mineral from the Murzinsk region in the Ural Mountains, Russia, was described and named ginzburgite (Voloshin et al. 1986) before it was realized that the type material also contained Be. The name ginzburgite is no longer used.
       
Crystal structure:  
  The structure of roggianite was first studied by Galli (1980) before the presence of Be was known. Even so, he determined the basic framework. This structure was revised and refined by Giuseppetti et al. (1991) on needle-shaped crystals from Pizzo Marcio, Val Vigezzo, Novara, Italy (Vezzalini and Mattioli 1979). The framework consists of highly ordered SiO4 (white in the accompanying diagram), AlO4 (light grey), and BeO4 (dark gray) tetrahedra. Chains of lau (4264) composite building units (Grice 2010) parallel to the c-axis. The lau building units are linked into a chain by sharing the four-ring faces. lau chains are linked through 3-rings containing two SiO4 tetrahedra and one Be-tetrahedron, each of which has two oxygen anions and two hydroxyls at the vertices (i.e. BeO2(OH)2).
  These hydroxyls interrupt the framework, but this type of structure has been included in the IMA system of zeolite nomenclature (Coombs et al. 1997). The linked lau chains form two kinds of channels parallel to the c-axis. One channel within 12-membered rings has an effective diameter of 4.2 Å, and contains loosely held H2O molecules (blue in the figure). The several different positions for H2O molecules, shown in figure, cannot be occupied simultaneously, limiting the cell content to 20 molecules (2.5 per formula unit). The other channels are along each side of the Be-tetrahedra, and contain Ca cations (orange) in eight-fold coordination with framework oxygen anions and hydroxyls. Roggianite
   
Chemical composition:
  The chemical compositions of roggianite from each of the three known occurrences are fairly similar. Elements other than the essential Ca, Be, Al, and Si, such as Na occur in small amounts. The water content of analyses from the Italian localities exceeds that possible in the structure (Giuseppetti et al. 1991). The H2O is given in all analyses as the total evolved during thermal gravimetric analysis.
   
Occurrences:
  Roggianite occurs as a secondary mineral in hydrothermally altered dikes. At both Alpe Rosso and Pizzo Marcio, Val Vigezzo, Novara, Italy, roggianite occurs as fibrous aggregates coating fractures of sodic feldspar dikes (albitite) that cut across greenschist and gneiss. A common associated mineral is thomsonite. In the Murinsk region, Urals, Russia, it occurs as spherulitic clusters in hydrothermally altered, desilicated pegmatite dikes. Common associated minerals are bavenite, bityite, behoite, analcime, phillipsite, and albite.
   
References:
  Coombs, D.S., Alberti, A., Armbruster, T., Artioli, G., Colella, C., Galli, E., Grice, J.D., Liebau, F., Mandarino, J.A., Minato, H., Nickel, E.H., Passaglia, E., Peacor, D.R., Quartieri, S., Rinaldi, R., Ross, M., Sheppard, R.A., Tillmanns, E., and Vezzalini, G. 1997. Recommended nomenclature for zeolite minerals: Report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. Can. Min., 35, 1571-1606.

Galli, E. 1980. The crystal structure of roggianite, a zeolite-like silicate. Proc. 5th Int. Conf. Zeolites. Heyden, London, 205-213.

Giuseppetti, G., Mazzi, F., Tadini, C., and Galli, E. 1991. The revised crystal structure of roggianite: Ca2[Be(OH)2Al2Si4O13]<2.5H2O. Neues Jahrb, Mineral., Monatsh., 1991, 307-314.

Grice, J.D. 2010. The role of beryllium in beryllosilicate mineral structures and zeolite formation. Can. Mineral. 48, 1492-1518.

Passaglia, E. 1969. Roggianite, a new silicate mineral. Clay Minerals, 8, 107-111.

Vezzalini, G. and Mattioli, V. 1979. Secondo ritrovammento della roggianite. Period. Mineral. 48, 15-20.

Volshin, A.V., Pakhomovskii, Ya.A., Rogachev, F.N., Tyusheva, F.N., and Shishkin, N.M. 1986. Ginzburgite--A new calcium-beryllium silicate from desilicated pegmatites. Mineralog. Zhurnal 8, 85-90. [Abs. Am. Mineral. 45, 439-440.]