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Hackly - Jagged, torn surfaces, (e.g. fractured metals).
Habit:
Acicular - Occurs as needle-like crystals.
Habit:
Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite)
Habit:
Reniform - "Kidney like" in shape (e.g.. hematite).
Hardness:
5-5.5 - Apatite-Knife Blade
Luminescence:
Non-fluorescent.
Luster:
Adamantine - Silky
Streak:
yellowish brown
Optical Properties of Goethite
Gladstone-Dale:
CI meas= -0.14 (Poor) - where the CI = (1-KPDmeas/KC) CI calc= -0.014 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.322,KPDmeas= 0.3618,KC= 0.3175 Ncalc = 2.05 - 2.37
Optical Data:
Biaxial (-), a=2.26-2.275, b=2.393-2.409, g=2.398-2.515, bire=0.1380-0.2400, 2V(Calc)=20-78, 2V(Meas)=0-27. Dispersion r > v extreme.
Pleochroism (x):
yellow or colorless.
Pleochroism (y):
brownish yellow or ocher yellow.
RL Anisotrophism:
Distinct in bluish grays.
RL Color:
Gray with bluish tint with yellow, red, brown internal reflections.
Reflectivity
Standardized Intensity (100%) Reflection Spectra of Goethite in Air
λ
R1
R2
∑ R1(λ)
∑ R2(λ)
400 nm
17.50
19.20
420 nm
16.70
18.30
440 nm
15.90
17.40
460 nm
15.20
16.70
480 nm
14.60
16.00
500 nm
14.10
15.50
520 nm
13.70
15.00
540 nm
13.30
14.60
560 nm
13.00
14.30
580 nm
12.80
14.00
600 nm
12.50
13.70
620 nm
12.40
13.50
640 nm
12.20
13.40
660 nm
12.00
13.20
680 nm
12.00
13.10
700 nm
11.90
13.00
Calculated Relative Intensity Colors of Goethite in Air
Relative Intensity
0%
70%
100%
140%
210%
280%
350%
420%
490%
560%
630%
680%
R1
R2
Calculated Properties of Goethite
Electron Density:
Bulk Density (Electron Density)=4.13 gm/cc note: Specific Gravity of Goethite =4.27 gm/cc.
Fermion Index:
Fermion Index = 0.01 Boson Index = 0.99
Photoelectric:
PEGoethite = 18.93 barns/electron U=PEGoethite x rElectron Density= 78.24 barns/cc.
Radioactivity:
GRapi = 0 (Gamma Ray American Petroleum Institute Units) Goethite is Not Radioactive
Goethite Classification
Dana Class:
06.01.01.02(06)Hydroxides and Oxides Containing Hydroxyl
Chemical Formula: 
