Heulandite
[(Ca,Na)2-3Al3(Al,Si)2Si13O36]*12H2O
Chemical name
Heulandite
Mineral name
Heulandite
Chemical formula
[(Ca,Na)2-3Al3(Al,Si)2Si13O36]*12H2O
Crystal system
monoclinic
Crystal Class
monoclinic-prismatic (2/m)
Space Group
C2/m
Unit cell
a [Å]:17.71
b [Å]:17.84
c [Å]:7.46
Formula units
Z=4
Frequent crystal surfaces
{010}, {100}, {001}, {20-1}, {110}, {111}
Twinning
on {100}
Mohs hardness
3.5 - 4
Density [g/cm3]
2.2
Cleavage
perfect on {010}
Fracture / Tenacity
subconchoidal to uneven
Color
colorless, white, gray, yellow, rose to red, orange, brown, black
Streak
white
Transparency
transparent to translucent
Optical character
biaxial (+)
Refractive Index
nα=1.476-1.506; nβ=1.479-1.510; nΥ=1.479-1.170
Birefringence δ
0.003 - 0.011