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
Approved IMA 2004 (Dana # Added)
Poudrette Quarry, Mont Saint-Hilaire, Rouville County, Quebec, Canada Link to MinDat.org Location Data.
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.
Skeletal - Crystals form crude outlines with missing faces.
5-6 - Between Apatite and Orthoclase
Optical Properties of Johnsenite-(Ce)
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
Uniaxial (-), e=1.637, w=1.648, bire=0.0110.
Calculated Properties of Johnsenite-(Ce)
Bulk Density (Electron Density)=3.06 gm/cc note: Specific Gravity of Johnsenite-(Ce) =3.19 gm/cc.
Fermion Index = 0.03 Boson Index = 0.97
PEJohnsenite-(Ce) = 96.52 barns/electron U=PEJohnsenite-(Ce) x relectron= 295.32 barns/cc.
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
100 gm / 3.91 cm
10 gm / 1.82 cm
1 gm / 8.43 mm
0.1 gm / 3.91 mm
0.01 gm / 1.82 mm
0.001 gm / 0.84 mm
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 (
** 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)