MINERAL: Siderophyllite (Mica group)
COLLECTION_LOCALITY: Brooks Mountains Seward Peninsula, AK
ORIGINAL_DONOR: National Museum of Natural History (Jim Crowley USGS)
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
40 kV - 30 mA and 6.5-9.5 keV (sidphyl.out, smear mount); 45 kV -
35mA and 7.3-9.5 keV (siphyl2.out, random or bulk mount)
References: Pattern for siderophyllite 1M in MSA Rev. Min. 13, p. 581; Huebner's reference patterns for micas
Found: trioctahedral 1M mica, subordinate chlorite and calcite (X-ray); immersion oil examination chlorite >= mica >>> carbonate
Sought: quartz [(101) reflection obscured; a very weak peak observed in the position of the quartz (100)]
Comments: At least three phases present. The mica pattern is consistent with siderophyllite. Sharp reflections suggest mica is well crystallized and compositionally homogeneous. The mica has a relatively large (002) spacing at 17.8, suggesting the presence of a large cation such as K. The chlorite (001) reflection is anomalously weak relative to the other chlorite reflections observed. Observed eight weak calcite reflections but found only a trace of carbonate in immersion oil, suggesting that the carbonate may not be homogeneously distributed.
J.S. Huebner and J. Pickrell,T. Schaefer, unpublished data, written communication, USGS, Reston, VA (1994)
COMPOSITIONAL_ANALYSIS_TYPE: NONE # XRF, EPMA, ICP(Trace), WChem
Since siderophyllite is volumetrically dominant according to my optical examination, its spectral signature will dominate over the chlorite. This probably also applies to the calcite. However, the spectrum looks strikingly similar to thuringite SMR-15 at wavelengths shorter than 2.0µm. The 2.3-µm region has small bands that are slightly shifted from thuringite (chlorite). This similarity may be coincidental, however, they may not be spectrally distinguishable at wavelengths short of 2.0µm. G. Swayze.
70 vol% Siderophyllite
15 vol% Chlorite
10 vol% Calcite
5 vol% Quartz
Siderophyllite is biaxial (-) with small 2V angle and has a dark green color in plain polarized light. Other gains with basal cleavage have a lighter 1st order gray interference color and also are biaxial (-) with a small 2V. Calcite and quartz are also present in minor amounts. G. Swayze.
SPECTRAL_PURITY: 1b2c3c4_ # NMNH104998 # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns