Low temperature zeolite found in a wide variety of geologic environments: volcanic rocks, metamorphic rocks, pegmatites, tuffs, and deep-sea sediments.
IMA Status:
Approved IMA 1998 (Dana # Added)
Locality:
Challis, Custer County, Idaho, U.S.A. Link to MinDat.org Location Data.
Name Origin:
Named after the English mineral collector, John Henry Heuland (1778-1856), a British mineral collector and dealer. The Na-dominant member of the heulandite series.
Brittle - Generally displayed by glasses and most non-metallic minerals.
Habit:
Crystalline - Coarse - Occurs as well-formed coarse sized crystals.
Habit:
Tabular - Form dimensions are thin in one direction.
Hardness:
3-3.5 - Calcite-Copper Penny
Luster:
Vitreous - Pearly
Streak:
white
Optical Properties of Heulandite-Na
Gladstone-Dale:
CI meas= 0.004 (Superior) - where the CI = (1-KPDmeas/KC) CI calc= -0.019 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.23,KPDmeas= 0.2248,KC= 0.2257 Ncalc = 1.49 - 1.5
Optical Data:
Biaxial (+), a=1.476-1.506, b=1.479-1.51, g=1.479-1.517, bire=0.0030-0.0110, 2V(Calc)=0-76, 2V(Meas)=10-48. Dispersion r > v.
Calculated Properties of Heulandite-Na
Electron Density:
Bulk Density (Electron Density)=2.22 gm/cc note: Specific Gravity of Heulandite-Na =2.20 gm/cc.
Fermion Index:
Fermion Index = 0.01 Boson Index = 0.99
Photoelectric:
PEHeulandite-Na = 1.81 barns/electron U=PEHeulandite-Na x relectron= 4.03 barns/cc.
Radioactivity:
GRapi = 11.50 (Gamma Ray American Petroleum Institute Units)
Concentration of Heulandite-Na per GRapi unit = 8.70 (%)
Estimated Radioactivity from Heulandite-Na - barely detectable
Chemical Formula: 
- barely detectable