Hornblende

This hornblende is from Lake Poway Park in Southern California. The straightish edges indicate a cleavage or parting plane.

Transmitted Off Crossed Circular Polarized Light

Definition/Function:

Hornblende is an amphibole series with the general chemical composition indicated as
Na_0-1Ca₂(Mg,Fe_3-5Al_2-0) [(Si_6-7Al_2-1)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.