Mineral - Heulandite-(Ca)
Heulandite-(Ca)
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
(Ca,Na)₅(Si₂₇Al₉)O₇₂ · 26H₂O
Unit Cell
a=17.77 b=17.95 c=7.44 β=116° 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
whitebrownredgreencolorless
Birefringence
0.009
Luster
Vitreous
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
C2/m (12)
Habit
leafy, tabular
Formation
(1) Hydrothermal, through crystallization from low-temperature, alkaline solutions in cavities in volcanic rocks (especially basalts), often as a late stage of rock alteration.
(2) Diagenetic, through the transformation of volcanic glasses (vitrite sands) or silicate sediments in the presence of pore-associated waters under zeolite facies conditions.
Paragenesis
Twinning
Rarity
Common
Synonyms
Heulandite-(Ca)
Composition
Elements
Mass
SiO₂
60.06
Al₂O₃
13.65
Fe₂O₃
1.16
MgO
0.38
CaO
4.44
SrO
1.35
BaO
0.75
Na₂O
1.07
K₂O
0.66
H₂O
15.54
Italy (Dana 1895)
Groups and Members
Zeolite-Group
Heulandite-Subgroup