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Clark et. al. 2003 USGS Open File Report 03-395
Spectral Library splib05a Sample Description

(For further information on spectrsocopy, see: http://speclab.cr.usgs.gov)

TITLE: Biotite HS28 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS28

MINERAL_TYPE: Phyllosilicate

MINERAL: Biotite (Mica group)

FORMULA: K(Mg,Fe+2)3(Al,Fe+3)Si3O10(OH,F)2

FORMULA_HTML: K(Mg,Fe+2)3(Al,Fe+3)Si3O10(OH,F)2

COLLECTION_LOCALITY: Ontario

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

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.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

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.

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: EM(WDA) # XRF, EM(WDS), ICP(Trace), WChem


COMPOSITION
KEYWORD
Oxide
ASCII
Amount Weight
Percent, %
Oxide
html
COMPOSITION: SiO2 38.00 wt% SiO2
COMPOSITION: TiO2 1.96 wt% TiO2
COMPOSITION: Al2O3 11.42 wt% Al2O3
COMPOSITION: FeO 17.44 wt% FeO
COMPOSITION: MnO .83 wt% MnO
COMPOSITION: MgO 13.85 wt% MgO
COMPOSITION: CaO .01 wt% CaO
COMPOSITION: Na2O .56 wt% Na2O
COMPOSITION: K2O 8.91 wt% K2O
COMPOSITION: Cl .06 wt% Cl
COMPOSITION: F 4.90 wt% F
COMPOSITION: Total 97.12 wt%
COMPOSITION: O=Cl,F,S 1.74 wt% #correction for Cl, F, S
COMPOSITION: New Total 95.38 wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Average of 6 samples. (Done by Gregg Swayze)

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

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.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1a2a3a4a # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns

LIB_SPECTRA_HED: where Wave Range Av_Rs_Pwr Comment
LIB_SPECTRA: splib04a r 690 0.2-3.0µm 200 g.s.= 300 µm
LIB_SPECTRA: splib05a r 1345 0.2-3.0µm 200 g.s.=


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