Mineral - Stilbite-(Ca)
Stilbite-(Ca)
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
NaCa₄(Si₂₇Al₉)O₇₂ · 28H₂O
Unit Cell
a=13.66 b=18.31 c=17.84 β=91° Z=4
Physical Properties
Hardness
3.5 - 4
Streak
white
Density
Normal (2-3,5)
Cleavage
Perfect after {010}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
grayorangeyellowcolorless
Birefringence
0.013
Luster
Vitreous
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
sheaf-shaped, massive, prismatic, radial, tabular
Formation
(1) Hydrothermal, formed by precipitation from low-temperature alkaline solutions within cavities (amygdules) in mafic volcanic rocks
(2) Metamorphic, formed by the alteration of plagioclase (zeolite facies)
Paragenesis
Twinning
Rarity
Common
Synonyms
Stilbite-(Ca)
Composition
Elements
Mass
SiO₂
52.70
Al₂O₃
17.71
CaO
7.76
Na₂O
2.39
K₂O
1.09
H₂O
18.40
Switzerland (Dana 1895)
Groups and Members
Zeolite-Group
Stilbite-Subgroup