TITLE: Antigorite NMNH96917 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: NMNH96917

MINERAL_TYPE: Phyllosilicate

MINERAL: Antigorite (Kaolinite-Serpentine group)

FORMULA: (Mg,Fe+2)3Si2O5(OH)4

FORMULA_HTML: (Mg,Fe+2)3Si2O5(OH)4

COLLECTION_LOCALITY: Rossa, Antigors Valley, Italy

ORIGINAL_DONOR: Smithsonian

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Polymorphous with Clinochrysotile, Lizardite, and Orthochrysotile.

The sample was ground in an alumina mortar and pestle and was wet sieved using methanol into <30µm (f), 30-45µm (e), 60-104µm (d), 104-150µm (c), 150-250µm (b) and >250µm (a) size fractions. (Letter denotes spectrum designation)

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Analysis by Gene Whitney, USGS Denver, indicate that the sample was representative of its structural class. Analysis by Norma Vergo indicate that the sample contains a medium amount of hornblende and other minerals. Hornblende is estimated to be 6-8 volume percent. Spectrally, the presence of hornblende is not believed to introduce specific absorption features to the antigorite, but may contribute to the general lowering of the reflectance at wavelengths less than 1.5µm.

King, T.V.V. and R.N. Clark, 1989, Spectral Characteriastics of Chlorites and Mg-Serpentines Using High-Resolution Spectroscopy. J. Geophys. Res., 13,997-14,008.

Clark, R.N., T.V.V. King, M. Klejwa, G. Swayze, and N. Vergo, 1990, High spectral resolution reflectance spectroscopy of minerals: J. Geophys Res. 12653-12680.

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: XRF # XRF, EM(WDS), ICP(Trace), WChem

COMPOSITION: SiO2 41.30 wt% SiO2
COMPOSITION: TiO2 0.15 wt% TiO2
COMPOSITION: Al2O3 1.59 wt% Al2O3
COMPOSITION: Fe2O3 3.61 wt% Fe2O3
COMPOSITION: FeO 4.51 wt% FeO
COMPOSITION: MnO 0.11 wt% MnO
COMPOSITION: MgO 36.30 wt% MgO
COMPOSITION: CaO 0.43 wt% CaO
COMPOSITION: Na2O 0.04 wt% Na2O
COMPOSITION: K2O 0.02 wt% K2O
COMPOSITION: H2O 11.19 wt% H2O
COMPOSITION: Total 99.26 wt%
COMPOSITION: O=Cl,F,S wt% #correction for Cl, F, S
COMPOSITION: New Total wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

This is an isochemical end member Mg-rich serpentine. Spectrally the mineral separates do not show absorptions due to any mineral species other than antigorite. See XRD discussion.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Platy habit, pale green color, 2 vol% white micaceous mineral that could be a variant of the green antigorite or a mineral contaminant, opaque inclusions altered to sesquioxides (total amount 3-5 vol% of grain volumes), first order gray interference color, moderate relief. All these properties are consistent with antigorite. G. Swayze

Grain size fraction 104-150 µm contained 8 vol% magnetite and 30 vol% clear feldspar?

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 502 0.2-2.7µm 200 a g.s.=1000µm
LIB_SPECTRA: splib04a r 514 0.2-2.7µm 200 b g.s.=165µm
LIB_SPECTRA: splib04a r 526 0.2-2.7µm 200 c g.s.=120µm
LIB_SPECTRA: splib04a r 538 0.2-2.7µm 200 d g.s.=70µm
LIB_SPECTRA: splib04a r 550 0.2-2.7µm 200 e g.s.=32µm
LIB_SPECTRA: splib04a r 562 0.2-2.7µm 200 f g.s.=15µm

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

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