Olivine dunite

Forstente. Pure forsterite is rare in nature. Most natural magnesium orthosilicates form solid solutions of fayalite, Fe2Si04, and forsterite. Forsterite refractories are usually made by calcining magnesium silicate rock such as dunite, serpentine, or olivine with sufficient magnesia added to convert all excess silica to forsterite and all sesquioxides to magnesia spinels. 

Rocks consisting essentially of olivine alone are known as dunites, the name coming from the occurrence of this rock in the Dun mountains of New Zealand. In the United States, this mineral is found in North Carolina, South Carolina, and Georgia, where corundum is associated wtith the dunite in commercial quantities. The olivine of peridotites alters readily to the mineral serpentine, often to such an extent that the rock itself is called a serpentine. As mentioned above, the pendotites may contain chromite or other valuable minerals, often to such an extent that they may be commercially exploited, for nickel, platinum, and precious garneL... 

Dunite An intrusive igneous rock that almost entirely consists of olivine, (Mg,Fe)2SiC>4. 

Fig. 15.3. Crustose lichen Lecidea lactea growing on dunite, a rock composed of the silicate olivine ((Mg, Fe)2Si04). Note dark stain (arrowed) below lichen representing amorphous silica coated in iron produced by lichen weathering (Purvis, 2000).

Chassigny is the only known martian dunite. It is an olivine-chromite cumulate consisting of 90% olivine (Fa. 32), 5% pyroxene, 2% feldspar (An 2o) that has been transformed into maskelynite, and 3% accessory minerals including chromite (Figure 30(d)). Melt inclusions in olivine contain hydrous amphibole. 

The silicates consist of mineral and lithic clasts set in a fine-grained fragmental to impact-melt matrix. The most common lithic clasts are basalts, gabbros, and orthopyroxenites, while dunites are minor and anorthosites are rare. The most common mineral clasts are centimeter-sized orthopyroxene and olivine fragments, while millimeter-sized plagioclase fragments are less common. 

The principal rock-type of the upper mantle comprising the minerals olivine and pyroxene. There are a number of different types of peridotite - see dunite,... 

Mantle rocks may be classified into those which are relatively enriched in the elements Ca, Al, Ti, and Na and those which are not. Lherzolites are "enriched" peridotites and are thought to be mantle rocks which have not melted and are known as "fertile" mantle -mantle from which a basaltic melt has not been extracted. Typically they contain a few percent of clinopyroxene and an aluminum-rich mineral (plagioclase, spinel, or garnet) in addition to the statutory olivine and orthopyroxene. Mantle which has experienced melt extraction is known as "depleted" mantle and has lower concentrations of the elements Ca, Al, Ti, and Na. This type of mantle is represented by the rock types harzburgite (peridotite without clinopyroxene and an aluminous mineral) and dunite. The relationship between a fertile mantle Iherzolite, depleted mantle harzburgite/ dunite and a basaltic melt is... 

Chassigny, the C of SNC, is a dunite, an olivine-rich rock that potentially comes... 

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