Hornblende
This hornblende is from the Cargille Standard Minerals set. This hornblende is pleochroic. If
a single linear polarizing filter is oriented with the vibration direction at right angles to the long axis of the grain, as is the case here,
then the grain is nearly colorless. If the polarizer in oriented with the vibration direction paralled to the long axis the grain is
blue-green.
Transmitted Single Linear Polarized Light Oriented Parallel to the Long Axis of the Crystal
Definition/Function:
Hornblende is an amphibole series with the general chemical composition indicated as
Na0-1Ca2(Mg,Fe3-5Al2-0)
[(Si6-7Al2-1)O22](OH,F)2. It is a very common mineral in plutonic igneous and metamorphic
rocks and sediments from those rocks.
Significance in the Environment:
Characteristic Features:
Hornblendes belongs to the monoclinic crystal system and are optically positive. Its refractive indices are 1.615-1.705, 1.618-1.714, and
1.632-1.730. Its birefringence ranges from 0.014 to 0.028. The density of hornblendes range from about 3.0 to 3.5 grams/cc. Small grains
are brown to green with the density of the color varying with iron content. Hornblende is pleochroic with alpha:light, beta:darker, gamma:darker
to much darker.
Associated Particles:
References:
Deer, W. A., R. A. Howie, and J. Zussman, AN INTRODCUTION TO THE ROCK-FORMING MINERALS, ISBN 0-582-30094-0, pp. 248-58, 1992.
