 |
Chemical Formula | The Olivine group is composed of three
minerals, with the following formulas: Forsterite = Mg2SiO4 Olivine (Chrysolite) = (Mg,Fe)2SiO4 Fayalite = Fe2SiO4 The intermediary variety, Olivine, is not scientifically recognized as a separate mineral, but is nevertheless mentioned. The mineral Tephroite (Mn2SiO4), which many consider a member of the Olivine group, forms a series with Forsterite. |
|
Composition | Magnesium iron silicate. The series ranges from the magnesium end member, Forsterite, through the intermediary member, Olivine (also known as Chrysolite), to the iron end member, Fayalite. |
|
Color | Olive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, white |
|
Streak | Colorless |
|
Hardness | 6½ - 7 |
|
Crystal Forms and Aggregates |
(Orthorhombic) Crystals, which are prismatic and stubby, are rare. Usually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses. |
|
Transparency | Transparent to translucent |
|
Specific Gravity | 3.2 - 4.2 |
|
Luster | Vitreous |
|
Cleavage | 2,1 ; 3,1- forming a 90º angle |
|
Fracture | Conchoidal |
|
Tenacity | Brittle |
|
Varieties |  Peridot - Green,
transparent gem variety Chrysolite - Yellow or yellow green Olivine.
Also a synonym for Olivine. Dunite
- Solid, grainy masses of Olivine. Usually classified as
a rock. Olivinoid
- Extraterrestrial form of Olivine found in meteorites |
|
In Group | Silicates ; Nesosilicates |
|
All About | The minerals compromising the Olivine group
are chemically and physically similar, and it is very
hard to distinguish one from the other. Therefore, these
minerals are rarely called by their real name, but are
just called "Olivine". Olivine is a very common mineral, but it rarely occurs in sizes larger than microscopic grains. For this reason, larger specimens are rare and sought after. Only few localities yield large examples of this mineral, although small grains are found worldwide. Olivine is also found in meteorites, and some large grains have been reported in many of them. |
|
Uses | The variety Peridot is a famous gem. It
creates a distinctive, yellow-green to olive-green gem
that is well known. It is the birthstone for August. Olivine is also used as a flux for making steel, and is an ore of magnesium. |
|
Striking Features | Color, localities, and hardness |
|
Complex Tests | Soluble in hydrochloric acid |
|
Popularity (1-4) | 1 |
|
Prevalence (1-3) | 1 |
|
Demand (1-3) | 1 |
|
Distinguishing Similar Minerals |
Tourmaline - occurs in different environments Apatite - softer (5) Garnet - occurs in different crystals, lacks cleavage Willemite - fluoresces green |
|
Commonly Occurs With |
Feldspar, Serpentine, Hornblende, Augite, Spinel, Diopside, Chromite, Iron-nickel |
|
Noteworthy Localities |
Olivine occurs worldwide, but only few
places yield large crystals. The finest Peridot comes
from St. Johns Island (Zebirget) in the Red Sea off
Egypt. Other Peridot localities include Mogok, Myanmar
(Burma); Soppat, Kohistan province, Pakistan; the Ural
Mountains of Russia; Snarum, Norway; Mt. Vesuvius, Italy;
and the Eifel District, Germany. In the U.S., Peridot is found near San Carlos (in the San Carlos Indian Reservation), Gila and Graham counties, Arizona. Large grains also occur near Fort Defiance (Buell Park and Garnet Ridge), Apache Co., Arizona; in the Kilbourne Hole, Dona Ana Co., New Mexico; in Webster, Jackson Co., North Carolina; and in the volcanic basalts of Hawaii. |
|
Picture Icon Links |
Sorry. No Images currently available. |
|
Picture Links | Sorry. No Images currently available. |
