U.S. Geological Survey home page

Clark et. al. 2003 USGS Open File Report 03-395
Spectral Library splib05a Sample Description

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

TITLE: Anthophyllite HS286 DESCRIPT



MINERAL_TYPE: Inosilicate

MINERAL: Anthophyllite (Amphibole group)

FORMULA: (Mg,Fe+2)7Si8O22(OH)2

FORMULA_HTML: (Mg,Fe+2)7Si8O22(OH)2


ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory


Forms series with Magnesio-anthophyllite and Ferro-anthophyllite.

Spectra for this sample were originally published in: 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.

With the note: "The dominant feature in its spectrum is the very well defined band at 0.95µm due to Fe+2 in the octohedral site, and this is accompanied by bands at 0.375, 0.475 and 0.65µm. The very weak 0.65µm band indicates the presence of a very little ferric iron which enters the mineral when aluminum substitutes for silicon. Bands at 1.4, 2.32, and 2.4µm are all due to the OH vibrations, and there is a complete absence of evidence for molecular H2O."

Sample measured for the library was the 74-250µm sieve interval, 3B.

Hunt et al. also noted some magnetite contamination, but with the high reflectance level at 1.6 µm it must be very low. Roger N. Clark



40 kV - 30 mA, 6.5-9.5 keV
File: anth286_mdi, *.out (smear mount on quartz plate)
References: Huebner's reference patterns; PDF2 #12-0242 21-1227; HS-286.3B (anth286b_MDI and anthp286_MDI)
Found: Talc, anthophyllite, minor 14 angstroms-chlorite, possible trace of mica

Comment: Talc peaks are strong and the basal reflections are very sharp; resolution of the alpha1-alpha2 reflections is good. Amphibole peaks are much less intense but sharp. Theses phases appear homogenous in composition and well crystallized. The amphibole is orthorhombic and its pattern is consistent with that of anthophyllite. (Comparison and random and smear mounts proves that talc is the dominant phase.) A minor chlorite phase displayed basal spacing's consistent with chamosite 1M or clinochlore 1M. A trace of mica (reflection at 10.4 angstoms) could not be further characterized. Very weak un indexed reflections at 8.6 and 7.4 angstoms. Very fine-grained sample.

40 kV -30 mA, 6.5-9.5 keV
File: anthp286_mdi, *.out (smear mount of 3B on quartz plate)
anth286b_mdi, *.out (edge/random mount of 3B)
anth286_mdi, *.out (smear mount of ground 4B)
References: JCPDS #13-558; Borg and Smith (1969); Huebner's reference patterns
Found: Talc, subordinate orthoamphibole, minor chlorite, trace mica (?), un indexed reflections of a minor phase(s) at 7.4 angstroms (weak intensity), 4.55 (strong, broad) 3.56 (medium), 2.63 (medium, broad), 2.49 (strong, broad), 2.45 (medium, broad), 2.23 (medium weak, broad), 1.42 (weak, broad)

Comment: Orthoamphibole pattern is consistent with anthophyllite or gedrite, but not with holmquistite. Chlorite identification based on three basal reflections; mica based on one basal reflection in a smear mount (this reflection is absent in a random mount). HS-286.3B extremely fine grained, like talcum powder; HS-286.4B is coarse but the grains are soft. Talc and chlorite reflections are sharp, suggesting good crystallinity. The orthoamphibole and the unidentified reflections are of variable sharpness.








Asbestiform crystal habit, pale color due to Fe-staining? Length slow, straight extinction. No twinning. These characteristics are consistent with anthophyllite. Grain size is that of clumps of fibres. G. Swayze




SPECTRAL_PURITY: 1c2_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 490 0.2-3.0µm 200 g.s.= 150 µm
LIB_SPECTRA: splib05a r 1112 0.2-3.0µm 200 g.s.=

USA.gov logo  Take Pride in America button