DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS326

MINERAL_TYPE: Inosilicate

MINERAL: Riebeckite (Amphibole group)

FORMULA: Na2Fe(+2)3Fe(+3)2Si8O22(OH)2

FORMULA_HTML: Na₂Fe₃⁺²Fe₂⁺³Si₈O₂₂(OH)₂

COLLECTION_LOCALITY: Colorado

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

"I-17 Riebeckite 326B--Colorado. Na₂Fe₃²⁺Fe₂³⁺- (Si₈O₂₂)(OH, F)₂: Riebeckite occurs in primary igneous rocks of acidic and intermediate composition. Ferric and ferrous iron produce the bands near 0.7µ and 0.975µ, and OH features appear at 1.4 and 2.35µ (again, there is a carbonate contribution to the latter band from slight calcite contamination). The small feature near 2.2µ is a hydroxyl-lattice combination band."

Sieve interval 74 - 250µm.

Hunt, G.R., J.W. Salisbury, and C.J. Lenhoff, 1973, Visible and near-infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology, v. 4, p. 85-106.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.0-9.5 keV
File: riebk326.mdi (smear on qtz plate)
References: PDF #23-1405, 45-1371, 33-1161, 21-1227; Borg and Smith (1969); Hawthorne (1981)
Found: Monoclinic amphibole, quartz, minor plagioclase, traces of chlorite and mica

Comments: Sharp peaks and good resolution of the alpha1-alpha2 components of the amphibole and quartz reflections suggest that these phases are well crystallized and that the amphibole is homogenous. Line-based search-match returns ferroan magnesiohornblende (45-1371), quartz, other amphiboles, and plagioclase feldspars. Profile based match-search returns quartz and the same magnesiohornblendeas likely hits. Manual overlays of magnesiohornblende (45-1371), quartz (22-1161), albite (10-0393) or anorthite (41-1481), mica such as 1M-phlogopite (10-0495), and chlorite such as chamosite (13-0029) account for all but one observed reflections, at 3.058 angstroms. Cell refinement, using the quartz peaks as an internal standard, result in a=9.852(4), b=18.123(10), c=5.292(4) angstroms and beta=104.86(6) degrees. These dimensions suggest that the M4 site is occupied by Ca or Ca+Na (Hawthorns, 1981, fig. 43). Retrieval from the PDF2 database using the cell dimensions returns actinolite (41-1366), ferrotschermakite (43-0665), kaersutite (44-1450), magnesiohornblende (45-1371), tremolite (44-1402), and winchite (20-1390). The cell dimensions of HS-326 were compared with those of many amphiboles in the PDF2 database. This comparison eliminated riebeckite, magnesioriebeckite, glaucophane, and eckermannite, or their solid solutions as possibilities. The amphibole in HS-236 can be a solid solution of the many remaining amphibole components. The plagioclase, chlorite, and mica components of the pattern are too weak for the determination of compostion or structure type.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE:

COMPOSITION_DISCUSSION:

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1_2_3_4_

LIB_SPECTRA_HED: where Wave Range Av_Rs_Pwr Comment

LIB_SPECTRA: splib04a r 4252 0.2-3.0µm 200 g.s.=

LIB_SPECTRA: splib05a r ____ 0.2-3.0µm 200 g.s.=

LIB_SPECTRA: splib06a r ____ 1.5-25µm 250 g.s.=