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(For further information on spectrsocopy, see:
http://speclab.cr.usgs.gov)
TITLE: Magnesite+Hydromagnesite HS47 DESCRIPT
DOCUMENTATION_FORMAT: MIXTURE
SAMPLE_ID: HS47
MIXTURE_TYPE: Intimate
MIXTURE: Magnesite + Hydromagnesite (Calcite group)
FORMULA: MgCO3 + Mg5(CO3)4(OH)2*4H2O
FORMULA_HTML: MgCO3 + Mg5(CO3)4(OH)2•4H2O
COLLECTION_LOCALITY: Victorville, CA
ORIGINAL_DONOR: Hunt and Salisbury Collection
CURRENT_SAMPLE_LOCATION: U.S.G.S. Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: U.S.G.S. Denver Spectroscopy Laboratory
SAMPLE_DESCRIPTION:
Forms series with Gaspeite and with Siderite.
Original spectrum published in:
Hunt, G.R., J.W. Salisbury, 1971, Visible and near-infrared
spectra of minerals and rocks: II. Carbonates. Modern
Geology, v. 2, p. 23-30.
With the following notes:
"Magnesite, MgCO3, is a carbonate mineral commonly found in
veins, and derived from the alteration of serpentine. Such
magnesites are compact and not recognizably crystalline.
Crystalline magnesite is found in sedimentary rocks, where it has
formed either by primary precipitation or by alteration of dolomite."
"This sample is of the compact, non-crystalline variety. It appears mineralogically pure in hand specimen, but its spectrum displays bands other than those due to the carbonate ion at the longer wavelengths. These bands near 1.4 and 1.9µm are due to water of hydration and so the sample must be, at least in part, composed of hydromagnesite, roughly Mg5(OH)2(CO3)4•4H2O. X-ray diffraction indicates only magnesite, but heating to 800°C shows the presence of 1.78% H2O by weight, confirming the presence of some water of hydration. The water band near 1.9µm precludes observation of the three weaker vibrational bands of the carbonate radical."
END_SAMPLE_DESCRIPTION.
XRD_ANALYSIS:
pure magnesite - Hunt and Salisbury as noted in above sample description.
40 kV - 30 mA, 6.5-9.5 keV
Reference: JCPDS #8-479
Found: Member of the calcite group, probably magnesite, plus at
least one additional, poorly crystallized phase.
Sought but not found: brucite
Comment: sharp pattern of crystalline carbonate closely matches
the JCPDS card for magnesite. I don't understand why
the (012) reflection is missing - but it doesn't appear
on the JCPDS card, either. There is a moderately weak,
broad peak (doublet) at 21 degrees 2 theta - thus the comment about
the additional phase. Could opaline silica be present??"
J.S. Huebner, J. Pickrell, and T. Schaefer , 1994, written communication.
END_XRD_ANALYSIS.
COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EM(WDS), ICP(Trace), WChem
COMPOSITION_TRACE:
COMPOSITION_DISCUSSION:
None.
END_COMPOSITION_DISCUSSION.
MICROSCOPIC_EXAMINATION:
END_MICROSCOPIC_EXAMINATION.
SPECTROSCOPIC_DISCUSSION:
END_SPECTROSCOPIC_DISCUSSION.
SPECTRAL_PURITY: 1a2_3_4_ # 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 2853 | 0.2-3.0µm | 200 | g.s.= |
| LIB_SPECTRA: | splib05a r 8596 | 0.2-3.0µm | 200 | g.s.= |
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