Olivine, Cargille Standard
This olivine is from The Cargille Standard Mineral set. The
lower gray particle is quartz in nearly an optic axis
orientation and not olivine. Some mixing of other minerals is not uncommon and
should be watched for.
Transmitted Off 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.
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. Hornblende is pleochroic with alpha and gamma:pale yellow
and beta:orange- yellow to riddish brown, depending on
iron content.
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.
