Olivine

Transmitted Crossed Circular Polarized Light

Definition/Function:

Olivine has the general chemical composition of (Mg,Fe)₂[SiO₄]. It is a very common mineral in igneous rocks and sediments from those rocks. The magnesium end member is the mineral Forsterite and the iron end member is Fayalite. As the amount of iron increases the names chrysolite, hyalosiderite, hortonolite, and ferrohortonolite are used.

The sands of Hawaii tend to be rich in olivines. The green sand beachs are dominated by olivine. The black sand beachs often have olivine inclusions in the black glass (obsidian) that makes up the beach.

Significance in the Environment:

Characteristic Features:

Olivines belong to the orthorhombic crystal system and may be optically positive or negative, the iron rich members being optically negative. The refractive indices range from 1.635-1.827 for alpha, 1.651-1.869 for beta, and 1.670-1.879 for gamma. Its birefringence ranges from 0.035 to 0.052. The density of hornblendes range from about 3.22 to 4.39 grams/cc. The 2V ranges from 82 to 134 degrees. Small grains tend to be colorless to green or yellow.

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. 3-13, 1992.