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Olivine is commonly recognized by it high retardation, distinctive fracturing, lack of cleavage, and alteration to serpentine. Colorless to olive green in thin section. Second-order interference colors.
There are at least two cleavages — i.e., the tendency to split along preferred crystallographic directions (perpendicular to the a and b axes in this case)—both of which are better-developed in the iron-rich varieties.
Forsterite is soluble in HCl, transparent to translucent, with perfect cleavage on {010} and imperfect cleavage on {100}, a vitreous to resinous/greasy luster, white streak, conchoidal fracture and a hardness of 6.5-7.0.
Photomicrograph of olivine under plane and under cross-polarized light with crystals showing second order interference colors. Note that olivine typically displays no distinct cleavage: Photomicrograph of olivine phenocrysts, in a matrix of Hawaiian basalt, in plane light.
Olivine altered to iddingsite within a mantle xenolith. Olivine is one of the less stable common minerals on the surface according to the Goldich dissolution series. It alters into iddingsite (a combination of clay minerals, iron oxides and ferrihydrite) readily in the presence of water. [30]
Consequently, olivine has no direction of good cleavage. Olivine is primarily an igneous mineral, crystallizing from high-temperature magmas. Its two most important end members, forsterite and fayalite, melt at different temperatures, and olivine’s crystallization behavior is similar to that of plagioclase.
The keys to identifying olivine are its high birefringence, lack of cleavage (but often having fractures), and alteration. Important properties: · Color - Usually colorless or very pale yellow. · Interference colors - Interference colors may range up to strong third order.
Olivine is a solid solution series mineral whose two most common end members are forsterite (Mg) and fayalite (Fe). This page concerns itself with olivine in general. If you need end member-specific information, please see the forsterite and fayalite pages.
Olivine is a silicate mineral with the general composition (Mg,Fe) 2 SiO 4. Having a very high crystallization temperature, it is formed early in the Bowen reaction series. It has no cleavage planes and is black to dark green in color.
The olivine can usually be identified by the presence of curved cracks, lack of cleavage and, in XP view, they often have bright interference colours - up to second-order blue (e.g. at coordinates 3200,2230).