A rare accessory mineral in granite and granite pegmatites.
IMA Status:
Approved IMA 1962
Locality:
In the USA, in a prospect pit about one km east of the Bassick mine, Querida, Wet Mountains, and at the Hardwick mine and Nightingale shaft, Custer Co., Colorado. Link to MinDat.org Location Data.
Name Origin:
To honor Maurice R. Brock, U.S. Geological Survey, who supplied the first specimen.
White, Light yellow, Dark reddish brown, Reddish brown.
Density:
3.7 - 4.1, Average = 3.9
Diaphaneity:
Translucent
Fracture:
Conchoidal - Fractures developed in brittle materials characterized by smoothly curving surfaces, (e.g. quartz).
Hardness:
3-4 - Calcite-Fluorite
Luster:
Vitreous - Greasy
Optical Properties of Brockite
Gladstone-Dale:
CI meas= 0.069 (Fair) - where the CI = (1-KPDmeas/KC) CI calc= 0.108 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.1689,KPDmeas= 0.1763,KC= 0.1893 Ncalc = 1.7 - 1.78
Optical Data:
Uniaxial (+), w=1.68, e=1.695, bire=0.0150.
Calculated Properties of Brockite
Electron Density:
Bulk Density (Electron Density)=3.60 gm/cc note: Specific Gravity of Brockite =3.90 gm/cc.
Fermion Index:
Fermion Index = 0.0003228265 Boson Index = 0.9996771735
Photoelectric:
PEBrockite = 753.16 barns/electron U=PEBrockite x relectron=2,710.28 barns/cc.
Radioactivity:
GRapi = 620,989.29 (Gamma Ray American Petroleum Institute Units)
Concentration of Brockite per GRapi unit =1,610.33 (PPB)
Brockite is Radioactive as defined in 49 CFR 173.403. Greater than 70 Bq / gram.
Estimated Exposure (mRem**)/hr If Held in Hand For One Hour
1000 gm / 7.88 cm
14,133,252
3.82E-04
620,989.29
204.16
100 gm / 3.66 cm
1,413,325
3.82E-05
62,098.93
20.42
10 gm / 1.70 cm
141,333
3.82E-06
6,209.89
2.04
1 gm / 7.88 mm
14,133
3.82E-07
620.99
0.20
0.1 gm / 3.66 mm
1,413
3.82E-08
62.10
0.02
0.01 gm / 1.70 mm
141
3.82E-09
6.21
0.00
0.001 gm / 0.79 mm
14
3.82E-10
0.62
0.00
Weight of pure Brockite in grams (gm) and Calculated Diameter of a Sphere with a Density of 3.90 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
Chemical Formula: 
- strong