Clark and others 2007 USGS Data Series 231
Spectral Library splib06a Sample Description

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

TITLE: Bytownite HS105 Plagioclase DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS105

MINERAL_TYPE: Tectosilicate

MINERAL: Bytownite (Plagioclase, Feldspar group)

FORMULA: (NaAlSi,CaAl2)Si2O8

FORMULA_HTML: (NaAlSi,CaAl₂)Si₂O₈

COLLECTION_LOCALITY: Essex County, New York

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Part of the albite-anorthite solid solution series.

Sieve interval 74 - 250µm.

IMAGE_OF_SAMPLE:
NO PHOTO

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV
File: labrd105.mdi
References: Borg and Smith (1969); Kroll (1983); PDF2 #41-1486, 19-0926
Found: Plagioclase feldspar, probably intermediate composition

Comments: Peaks are moderately sharp peaks but show poorly resolved alpha1-alpha2 components, perhaps due to some variation in composition or structural state. Line-based search-match returns 10 plagioclase feldspars in the first 10 hits; the most likely hit (and only feldspar) from profile-based search-match is #41-1481, disordered An83Ab17 (bytownite). The delta 2 theta(131)-(1-31)=1.82 degrees and corresponds to low plagioclase (or intermediate albite) structural state and composition less than 53% anorthite component (Kroll, 1983, fig. 12). Reflections diagnostic of low plagioclase composition (Kroll, 1983, p. 328-9) yield Si/Al=1.3:1 (bytownite composition). There were unindexed reflections: 8.55 Angstroms (weak) is observed in other patterns and may be instrumental in origin; 4.23 Angstroms (very weak) could be explained by a trace of K-feldspar; and 1.829 Angstroms (moderately weak) remains unexplained.

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EM(WDS), ICP(Trace), WChem
COMPOSITION_TRACE:

None

COMPOSITION_DISCUSSION:

Hunt and Salisbury originally considered this sample to be a labradorite.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Not done yet

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1b2b3b4b # 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 2685	0.2-3.0µm	200	g.s.=
LIB_SPECTRA:	splib05a r 1451	0.2-3.0µm	200	g.s.=
LIB_SPECTRA:	splib06a r 4002			g.s.=
LIB_SPECTRA:	splib06a r 4014			g.s.=