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Fischer K F , American Mineralogist , 51 (1966) p.814-818, A further refinement of the crystal structure of cummingtonite, (Mg,Fe)7(Si4O11)2(OH)2
Granular - Generally occurs as anhedral to subhedral crystals in matrix.
Hardness:
5-6 - Between Apatite and Orthoclase
Luminescence:
Non-fluorescent.
Luster:
Vitreous - Silky
Streak:
grayish white
Optical Properties of Cummingtonite
Gladstone-Dale:
CI meas= 0.04 (Good) - where the CI = (1-KPDmeas/KC) CI calc= -0.125 (Poor) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2341,KPDmeas= 0.1999,KC= 0.2082 Ncalc = 1.6 - 1.75
Optical Data:
Biaxial (+), a=1.639-1.671, b=1.647-1.689, g=1.664-1.708, bire=0.0250-0.0370, 2V(Calc)=70-90, 2V(Meas)=65-90. Dispersion r > v or r < v.
Pleochroism (x):
colorless, colorless, or pale yellow.
Pleochroism (y):
colorless, pale yellow, or pale brown.
Calculated Properties of Cummingtonite
Electron Density:
Bulk Density (Electron Density)=3.35 gm/cc note: Specific Gravity of Cummingtonite =3.35 gm/cc.
Fermion Index:
Fermion Index = 0.03 Boson Index = 0.97
Photoelectric:
PECummingtonite = 1.59 barns/electron U=PECummingtonite x rElectron Density= 5.33 barns/cc.
Radioactivity:
GRapi = 0 (Gamma Ray American Petroleum Institute Units) Cummingtonite is Not Radioactive