Stellerite |(Ca)4(H2O)28| [Al8Si28O72]
  Orthorhombic, mmm, platy crystals with prominent {010} face, modified by {100}, {001} {111}
Physical properties:
  Cleavage: {010} perfect.
Hardness:  4 – 4.5
D: 2.13 gm/cm3.
Luster: vitreous, pearly on {010}.
Streak: white
  Stellerite, 3 cm long crystal from the Garawilla Volcanics, Tambar Springs, New South Wales, Australia. © Volker Betz.
Optical properties:            
  Color: colorless to white; colorless in thin section.
Biaxial (-).
α = 1.485, β = 1.496, γ = 1.498, δ = 0.013, 2Vx  = 45°. a = X, b = Y, c = Z.
  Unit cell data:
13.600,  b  18.222,  c  17.863 Å.
Z = 2, Space group Fmmm
  Stellerite was named and described by Morozewicz (1909) for material found on Commander Island, Bering Sea. It is named after Wilhelm Steller (1709-1746), natural scientist and military doctor who made important observations on Commander Island. Stellerite
Crystal structure:

The framework topology of stellerite is the same as stilbite (STI), and with mostly Ca in the channels is orthorhombic, space group Fmmm (Galli and Alberti 1975, Miller and Taylor 1985). The neutron diffraction data of Miller and Taylor (1985) disclosed slight (Si,Al) ordering with individual tetrahedral Al contents ranging from 10 to 30%.
 Stellerite has only one fully, or nearly fully occupied, Ca channel cation site (red) (Galli and Alberti 1975, Miller and Taylor 1985). Ca is coordinated only to channel H2O molecules (blue) and not to framework oxygens. Similar to stilbite, the Ca(H2O) complex is hydrogen bonded to the framework oxygens (Miller and Taylor 1985). There are seven partially occupied H2O sites in the structure with occupancies between 0.2 and 0.8 (Galli and Alberti 1975, Colella and Gualtieri, 2007).

Chemical composition:
  Stellerite shows little variation around the average 28 Si per cell. Ca is the dominant non-framework cation with minor amounts of Na; K occurs rarely, while other elements like Mg, Sr, and Ba are absent or very minor in amount. As shown by Passaglia et al. (1978) there is no compositional gap between stellerite and stilbite
  Distinguishing stellerite from stilbite requires a careful chemical analysis, a good X-ray powder pattern, and optical examination. Stellerite should have less than about 0.2 Na atoms per formula unit (72 oxygens), no splitting of the 204 peak (in the interval 23 to 24° 2θ, CuKα) in the X-ray pattern, and optically straight extinction with no twinning.
  Diagenesis and alteration of mafic lava flows.
Several of the known stellerite occurrences are in cavities of basalt. The type locality on Copper Island, Commander Islands (Kommandorskiye Ostrova), Russia, Bering Sea, is in brecciated basaltic rocks. Galli and Passaglia (1973) describe stellerite from lower Miocene andesitic breccia, exposed near Villanova Monteleone, Sardinia, Italy. Large crystals of stellerite occur in the Garrawilla Volcanics (Jurassic flows interbedded in sandstone), New South Wales, Australia (England and Sutherland 1988). Exceptional specimens have been found at Jalgaon, Maharashtra, India. There are no clear indications of why stellerite crystallized in these localities rather than stilbite-Ca, except for the lack of Na.

Hydrothermal systems.
The occurrences of stellerite in plutonic and metamorphic rocks are so similar to those of stilbite-Ca that paragenesis cannot be used to distinguish the two minerals. Like stilbite, stellerite occurs in some hydrothermal ore veins. One notable example is east of Kuruna, Sweden, at the old copper mine next to the Leveäniemi mine. This is the locality of the mineral, for which the name zeolite was first coined (Cronstedt 1756, Colella and Gualtieri 2007).

Stellerite occurs in alteration cavities in pegmatite near Dassau, Baltistan, Northern Territories, Pakistan. Among many occurrences of stellerite in retrograde vein fillings cutting metamorphic rocks, the following are examples: at the Malmberget Iron Mine, Lappland, Sweden (Passaglia et al. 1978); in granitic gneiss at Siglitztal near Brokstein, Austria (Passaglia et al. 1978). Stellerite occurs as a low temperature alteration product along fractures in several kinds of metamorphic rocks: in alpine-clefts in the granitic gneiss of the Aar Massif, Switzerland (Armbruster et al. 1996), in thin veins in dioritic and granitic gneiss at Kongsberg, Norway (Neumann 1944); in schists on the island of Magerø, Norway (Saebø et al. 1959); in the calc‑schist of Val Varenna, Liguria, Italy (Pelloux 1949); and in an granite porphyry in China (Young 1965).
  Armbruster, T., Kohler, T., Meisel, T., Nägler, T., Götzinger, M.A., Stalder, H.A. 1996. The zeolite, fluorite, quartz assemblage of the fissures at Gibelsbach, Fiesch (Valais, Switzerland): crystal chemistry, REE patterns, and genetic speculations. Schweiz. Mineral. Petrogr. Mitt. 76, 131-146.

Cronstedt, A.K. 1756. [Observation and description of an unknown kind of rock to be named zeolites] Kongl. Vetenskaps Acad. Handl. Stockholm. 17, 120-3 (in Swedish).

Colella, C. and Gualtieri, A.F. 2007. Cronstedt’s zeolite. Microporous Mesoporous Mater. 105, 213-221.

England, B.M.,  Sutherland, F.L. 1988.  Volcanic zeolites and associated minerals from New South Wales Min. Rec., 19, 389-406.

Galli, E. and Alberti, A. 1975. The crystal structure of stellerite. Bull. Soc. fr. Minéral. Cristallogr. 98, 11-18.

Miller, S.A. and Taylor, J.C. 1985. Neutron single-crystal diffraction study of an Australian stellerite. Zeolites, 5, 7-10.

Morozewicz, J. 1909. Über Stellerit, ein neues Zeolithmineral. Bull. International de l’Académie des Sciences de Cracovie, 344-359.

Neumann, H. 1944. Silver deposits at Kongsberg. Norg. Geol. Unders. 162, 1-133

Passaglia, E., Galli, E., Leoni, L. and Rossi, G. 1978. The crystal chemistry of stilbites and stellerites. Bull. Minéral. 101, 368-375.

Pelloux, A. 1949. Sopra alcune zeoliti della Valle del Varenna presso Pegli con descrizone di un minerale nuovo per l’Italia. Ann. Mus. Civ. Stor. Nat. Genova, 63, 1-8.

Saebø, P.C., Reitan, P.H., and Gaul, J.J.C. 1959. Stilbite, stellerite and laumontite at Honningvag, Northern Norway. Norg. Geol. Unders., 205, 171-173.

Young, M. 1965. Stellerite and its genesis in a disseminated molybdenum ore. Sci. Geol. Sin. 3, 295-302.