MINERAL: Epidote (Epidote group)
ORIGINAL_DONOR: Hunt and Salisbury Collection
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
Forms series with Clinozoisite.
"S-3 Epidote 328B--Arizona. Ca2(Al,Fe)Al2O• OH(Si2O7)(SiO4): This metamorphic mineral is the iron-rich end member of the clinozoisite-epidote series. The features are those due to both ferrous and ferric iron at 0.41, 0.47, near 0.6 µ and 1.0 µ. Again, the hydroxyl features are unusual. The feature at 1.55 µ appears, and it is accompanied by a very weak feature at 1.4 µ (not discernible in reproduced spectrum). The two features near 1.85 µ and 1.9 µ, like those in zoisite, are apparent, as is a very intense feature at 2.35 µ with well defined side features."
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.
Grain size fractions are indicated by the extension after the sample number:
.3B = 74-250 µm
Spectrally pure. Epidote plus a large amount of quartz plus a small amount other; M: ~2% magnetite on epidote, ~15% quartz, ~3% plagioclase, no carbonate. (Norma Vergo)
COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem
80 vol% epidote
15 vol% quartz
3 vol% plagioclase ?
2 vol% magnetite
average grain size= 250 µm
Epidote grains are highly fractured or polygranular, with quartz intergrowths on about 10% of epidote grains. Individual crystal grain size is about 50 µm or less because of polygranular and fractured nature. Determination of optical properties is difficult because of fractures and polygranular nature.
SPECTRAL_PURITY: 1c2b3c4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns