SAMPLE_ID: HS47.1B, HS47.2B, HS47.3B, HS47.4B
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
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."
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.
Magnesite is major phase with minor amount of clay (most likely expandable smectite); no hydromagnetsite was detectable with XRD. B. Benzel. 2016
COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem
SPECTROSCOPIC_DISCUSSION: Broad absorptions at 1.54 and 2.0 microns suggest hydrogen bonded structural water most likely as a component of hydromagnesite. It is unlikely that smectite can account for the long-wavelength position of these broad intense absorptions. G. Swayze.
SPECTRAL_PURITY: 1a2_3_4_ # HS47.1B # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns
SPECTRAL_PURITY: 1a2_3_4_ # HS47.2B # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns
SPECTRAL_PURITY: 1a2a3a4_ # HS47.3B # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns
SPECTRAL_PURITY: 1a2_3_4_ # HS47.4B # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns