MINERAL: Biotite (Mica group)
ORIGINAL_DONOR: Hunt and Salisbury Collection
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
Forms series with Phlogopite.
Usually in irregular foliated masses. Composition is similar to phlogopite but with considerable substitution of Fe+2 for Mg. There is also substitution by Fe+3 and Al for Mg and by Al for Si. In addition a series exists between phlogopite and biotite. The trioctahedral biotite structure is the same as that of phlogopite.
"S-5. Biotite. Bancroft, Ontario (28). A potassium magnesium-iron-aluminum silicate, essentially K(Mg,Fe)3AlSi3O10(OH)2. Biotite is a widely distributed accessory mineral in igneous rocks and also occurs in some metamorphic rocks. Ferrous and ferric ions cause a very broad band in the 0.6 to 1.5µm region, and the drop-off in the blue. Hydroxyl bands are barely observable in the spectra. There are several possible reasons for the lack of observable OH overtones in this spectrum: The OH groups are commonly oriented (because the mica flakes lie on their cleavage faces) so that the observation angle may preclude their observation in the spectrum; the fundamental OH stretch is normally much broader in biotite than in other micas; and the OH concentration in this sample may be particularly low, because the OH in biotite may be readily replaced by F, Na, Fe+2 etc."
Sieve interval 74 - 250µm.
Hunt, G.R., J.W. Salisbury, 1970, Visible and near-infrared spectra of minerals and rocks: I. Silicate minerals. Modern Geology, v. 1, p. 283-300.
N. Vergo: Biotite plus trace other (pre 1990). New analysis by Steve Sutley, September, 2003 shows this is a pure titanium biotite. Thus, the spectral purity is raised from b to a.
Clark, R.N., King, T.V.V., Klejwa, M., Swayze, G.A., and Vergo, N., 1990, High spectral resolution reflectance spectroscopy of minerals: Journal of Geophysical Research, v. 95, no. 8B, p 12,653-12,680.
COMPOSITIONAL_ANALYSIS_TYPE: EM(WDA) # XRF, EPMA, ICP(Trace), WChem
|COMPOSITION:||O=Cl,F,S||1.74||wt%||#correction for Cl, F, S|
Average of 6 samples. (Done by Gregg Swayze)
Basal cleavage, slight pleochroism, pale green color, no mottled extinction, 1st order gray interference color, rod like inclusions (1-2 vol% sillimanite, length slow, straight extinction), biaxial (-), 2v about 30 degrees. Apart from lack of mottled extinction and low order interference color, all is consistent with this sample being biotite. G. Swayze.
SPECTRAL_PURITY: 1a2a3a4a # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns