Occurs intergrown with zirsilite-(Ce) in a cavity near the margin of a marble xenolith in an igneous breccia along the contact between porphyritic nepheline syenite and sodalite sye nite. Eudialyte group
IMA Status:
Approved IMA 2004 (Dana # Added)
Locality:
Poudrette Quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada Link to MinDat.org Location Data.
Name Origin:
Named for Ole Johnsen (b. 1940), of the Geological Museum, University of Copenhagen, Denmark, and for his extensive research into the eudialyte group.
Brittle - Uneven - Very brittle fracture producing uneven fragments.
Habit:
Skeletal - Crystals form crude outlines with missing faces.
Hardness:
5-6 - Between Apatite and Orthoclase
Luster:
Vitreous (Glassy)
Streak:
white
Optical Properties of Johnsenite-(Ce)
Gladstone-Dale:
CI meas= 0.01 (Superior) - where the CI = (1-KPDmeas/KC) CI calc= 0.007 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2014,KPDmeas= 0.2008,KC= 0.2029 Ncalc = 1.65
Optical Data:
Uniaxial (-), e=1.637, w=1.648, bire=0.0110.
Calculated Properties of Johnsenite-(Ce)
Electron Density:
Bulk Density (Electron Density)=3.06 gm/cc note: Specific Gravity of Johnsenite-(Ce) =3.19 gm/cc.
Fermion Index:
Fermion Index = 0.03 Boson Index = 0.97
Photoelectric:
PEJohnsenite-(Ce) = 96.52 barns/electron U=PEJohnsenite-(Ce) x relectron= 295.32 barns/cc.
Radioactivity:
GRapi = 6,454.67 (Gamma Ray American Petroleum Institute Units)
Concentration of Johnsenite-(Ce) per GRapi unit = 154.93 (PPM)
Johnsenite-(Ce) is Radioactive as defined in 49 CFR 173.403. Greater than 70 Bq / gram.
Estimated Radioactivity from Johnsenite-(Ce) - mild
Specimen Size Weight/Volume (Sphere) *
Calculated Activity Bequerols (Bq)
Calculated Activity Curies (Ci)
Estimated Activity GR(api)
Estimated Exposure (mRem**)/hr If Held in Hand For One Hour
1000 gm / 8.43 cm
141,328
3.82E-06
6,454.67
2.12
100 gm / 3.91 cm
14,133
3.82E-07
645.47
0.21
10 gm / 1.82 cm
1,413
3.82E-08
64.55
0.02
1 gm / 8.43 mm
141
3.82E-09
6.45
0.00
0.1 gm / 3.91 mm
14
3.82E-10
0.65
0.00
0.01 gm / 1.82 mm
1
3.82E-11
0.06
0.00
0.001 gm / 0.84 mm
0
3.82E-12
0.01
0.00
Weight of pure Johnsenite-(Ce) in grams (gm) and Calculated Diameter of a Sphere with a Density of 3.19 gm/cc.*
Goverment Estimate of Average Annual Exposure (
360 mRem)
** Note: 10 microsieverts/hr = 1 mRem/hr **
Max Permissable Adult Dose 50,000 mRem/yr (hands), 15,000 mRem/yr (eyes)
Lethal Dose LD(50) Exposure 400,000 to 500,000 mRem
Estimated Thorium Activity ( 0.32 % Th) From Sum REE Elements ( 6.30 % REE)
Chemical Formula: 
- mild