Sample Description USGS Spectral Library Version 7

USGS Spectral Library Version 7 Sample Description

Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., Driscoll, R.L., and Klein, A.J., 2017, USGS Spectral Library Version 7: U.S. Geological Survey Data Series 1035, 61 p., https://doi.org/10.3133/ds1035
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TITLE: Nepheline HS19 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS19.1B, HS19.3

MINERAL_TYPE: Tectosilicate

MINERAL: Nepheline (Nepheline group)

FORMULA: (Na,K)AlSiO4

FORMULA_HTML: (Na,K)AlSiO₄

COLLECTION_LOCALITY: Bancroft, Ontario

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

"S-13. Nepheline. Bancroft, Ontario (19). This sodium-potassium aluminum silicate, (Na,K)(Al,Si)₂O₄, is found in igneous rocks whose magmas contained insufficient silica to combine with the soda present to form feldspar. This nepheline sample illustrates very clearly the effect of grinder steel contamination. Note that the two contaminated finer particle size fractions have both reduced reflectivity and their near-infrared bands eliminated. In contrast, the uppermost curve of uncontaminated 0.5µ nepheline is both highly reflective and retains its spectral features. The bands near 1.4, 1.9 and 2.5µ are due to water, presumably present as fluid inclusions in microscopic vesicles within the nepheline. The water is not present as part of the nepheline lattice, and the only contaminant (a very small amount of biotite) would not produce these bands."

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.

Grain size fractions are indicated by the extension after the sample number:
.1B = <5 µm
.3 = 74-250 µm

IMAGE_OF_SAMPLE:
NO PHOTO

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV
Files: nephlin19.out, -.mdi, fine (.1B) fraction, ground once; nephl19b.*, fine fraction not ground; nephl19c.*, 70-250 micrometer fraction (.3) ground once
References: Borg and Smith (1969) for nepheline; JCPDS 25-776 and 24-176 (cancrinite), 37-476 (sodalite); Huebner's reference patterns; Deer and others (1963, vol. 4)
Found: Nepheline with Na/(Na+K)= approximate 0.75, trace phlogopite; traces of cancrinite (probable), sodalite (possible).

Comment: HS-19.3 gives an exceptionally well-crystallized pattern. Unindexed reflections at 5.64, 4.03, 3.44, 2.94, and 2.81 may prove to be nepheline peaks that are too weak to be reported in the literature.

J.S.Huebner, J. Pickrell, T. Schaefer, written communication 1994

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1c2_3_4_ # HS19.1B # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns
SPECTRAL_PURITY: 1c2b3c4_ # HS19.3 # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns