Bellbergite

Formula:  (K,Ba,Sr)₂Sr₂Ca₂(Ca,Na)₄Al₁₈Si₁₈O₇₂ ^. 30H₂O

Origin of name:  After locality; Bellerberg (also Bellberg) volcano, 2 km north of Mayen, Eifel, Germany

Crystal system:  Hexagonal

Crystal class:  6mm or -6m2 or 6/m 2/m 2/m

Twinning:

Unit cell: a = 13.244 Å, c = 15.988 Å

Colour:  Colourless, White

Diaphaneity:  Transparent

Luster:  Vitreous

Habit:  Subhedral intergrowths, elongate {0001}; rarely well formed dipyramids, up to 0.3 mm

Hardness:  5

Specific gravity:  2.20

Cleavage:  None

Tenacity: conchoidal fracture

Streak:  White

Synonyms/varieties:

Comments: Zeolite group. Found in leucite tephrite lava at contacts between lava and calcium-rich xenoliths