OCCURRENCE AND USES OF OLIVINE

Olivine, a naturally occurring ferro-magnesium orthosilicate [(Mg,Fe)₂SiO₄], is a common constituent in ultramafic rocks. For the past several decades, ultramafic rocks in western North Carolina have been the leading domestic source of olivine. Economic deposits of olivine in western North Carolina occur as alpine-type ultramafic bodies within the Blue Ridge province. Many studies reported in the geologic literature conclude that these ultramafic bodies were originally formed as oceanic crust and tectonically incorporated into their present terranes during early stages of the Paleozoic Appalachian orogenies. As a result of subsequent metamorphic events most of the ultramafic bodies in the Appalachians show varying degrees of secondary alteration of the olivine to assorted accessory phases. However, several of the larger ultramafic bodies show only minor alteration such that the olivine content is greater than 90%.

There is complete solid solution between the Mg-end member (Forsterite) and the Fe-end member (Fayalite). The end member concentration affects the physical properties of olivine, which affects the suitability for various industrial applications. The higher magnesium-olivine has a higher melting temperature than the more iron-rich end member. Forsterite content of olivine in the western North Carolina deposits tends to average greater than Fo₉₀, making it suitable for refractory olivine.

Due to the refractory characteristics of olivine, the primary uses are for foundry and refractory applications in the steel industry. Other applications include use as an abrasive, particularly as a sand blasting agent. The use as a sand blasting agent is attractive because of the general absence of free silica in naturally occurring olivine deposits. Recent investigations have also evaluated the use of olivine as a source for CO₂ sequestration.