MINERAL: Ferro-Hornblende (Amphibole group)
COLLECTION_LOCALITY: Brewster, New York
ORIGINAL_DONOR: Hunt and Salisbury Collection
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
Forms series from Magnesiohornblende to Ferrohornblende.
"S-1E. Amphibole, variety Hornblende. Brewster, N.Y., (115B). This is an impure sample, deep green in color. It displays the double band structure in the 0.6 to 1.1 µ region that is typical of the presence of both the ferric and ferrous ion. The presence of a light gray contaminant (muscovite) raises the reflectivity of the sample which is most obvious in the largest size range, and explains the anomalous (lighter?) reflectivity of that size fraction. The hydroxyl bands are not so strong as in tremolite and actinolite, which is typical of hornblende. The very weak bands in the visible near 0.5, 0.45, and 0.5 µ are due to both the ferrous and ferric ions."
Hunt, G.R., J.W. Salisbury, 1970, Visible and near-infrared spectra of minerals and rocks: I. Silicate minerals. Modern Geology, v. 1, p. 283-300.
Grain size fractions are indicated by the extension after the sample number:
.3B = 74-250 µm
40 kV - 30 mA, 6.5-9.5 keV
File: hnbld115.out, -.mdi
References: Borg and Smith (1969)
Found: Clinoamphibole, minor mica, trace chlorite
Comment: Pattern matches that of tremolite more closely than hornblende.
J.S. Huebner, J. Pickrell, T. Schaefer, written communication(USGS)
COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem
90 vol% Hornblende
8 vol% plagioclase + quartz + other (uniaxial -)
1 vol% mica (clear)
1 vol% calcite (fizz with HCl)
average grain size = 250 µm
Smaller grains ~5 µm coat larger grains @ 30% surface area. Hornblende has inclined extinction (19 ° for OAP ll (010)), biaxial (-), strong green-blue pleochroism, and amphibole cleavage. All these properties are consistent with this sample being mostly hornblende. Heavy liquid or Franz separation may sort impurities out. G. Swayze.
SPECTRAL_PURITY: 1c2c3b4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns