In "opal" veinlets in rhyolite and agglomerates, as well as in sandstones and limestones.
IMA Status:
Approved IMA 1960
Locality:
Autunite No. 8 claim, Thomas Range, Juab County, Utah, USA. Link to MinDat.org Location Data.
Name Origin:
Named for Mary Alice Dowse Weeks (1909-1988), mineralogist with the U.S. Geological Survey, noted specialist in the mineralogy of uranium and vanadium.
Bladed - Aggregates of thin lath-like crystals (e.g. kyanite).
Habit:
Platy - Sheet forms (e.g. micas).
Hardness:
1-2 - Between Talc and Gypsum
Luminescence:
Radioactive.
Luster:
Waxy
Streak:
yellow
Optical Properties of Weeksite
Gladstone-Dale:
CI meas= -0.041 (Good) - where the CI = (1-KPDmeas/KC) CI calc= -0.136 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.16,KPDmeas= 0.1467,KC= 0.1409 Ncalc = 1.53 - 1.58
Optical Data:
Biaxial (-), a=1.596, b=1.603, g=1.606, bire=0.0100, 2V(Calc)=66, 2V(Meas)=~60. Dispersion r > v strong.
Pleochroism (x):
colorless.
Pleochroism (y):
pale yellow green.
Pleochroism (z):
yellow green.
Calculated Properties of Weeksite
Electron Density:
Bulk Density (Electron Density)=3.62 gm/cc note: Specific Gravity of Weeksite =4.10 gm/cc.
Fermion Index:
Fermion Index = 0.01 Boson Index = 0.99
Photoelectric:
PEWeeksite =1,266.86 barns/electron U=PEWeeksite x relectron=4,588.80 barns/cc.
Radioactivity:
GRapi = 3,658,435.27 (Gamma Ray American Petroleum Institute Units)
Concentration of Weeksite per GRapi unit = 273.34 (PPB)
Weeksite is Radioactive as defined in 49 CFR 173.403. Greater than 70 Bq / gram.
Estimated Radioactivity from Weeksite - very strong
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 / 7.75 cm
86,962,009
2.35E-03
3,658,435.27
1,202.77
100 gm / 3.60 cm
8,696,201
2.35E-04
365,843.53
120.28
10 gm / 1.67 cm
869,620
2.35E-05
36,584.35
12.03
1 gm / 7.75 mm
86,962
2.35E-06
3,658.44
1.20
0.1 gm / 3.60 mm
8,696
2.35E-07
365.84
0.12
0.01 gm / 1.67 mm
870
2.35E-08
36.58
0.01
0.001 gm / 0.78 mm
87
2.35E-09
3.66
0.00
Weight of pure Weeksite in grams (gm) and Calculated Diameter of a Sphere with a Density of 4.10 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
Weeksite Classification
Dana Class:
53.03.02.01(53)Nesosilicate Insular SiO4 Groups and Other Anions of Complex Cations
Chemical Formula: 
- very strong