مینرال­ های گروه سیلیمانیت؛ سیلیمانیت، کیانیت و آندالوزیت

The Sillimanite Minerals: Andalusite, Kyanite, and Sillimanite

 مینرال­ های گروه سیلیمانیت؛

سیلیمانیت، کیانیت و آندالوزیت

ABSTRACT

The chemistry and the mineralogy of the three Al2O3.SiO2 sillimanite minerals (anadlusite, kyanite, and sillimanite) are described. Their P–T diagram is discussed. The structural differences among the three are reviewed, emphasizing the coordination of the Al3+ cations that link the double octahedral chains within the structures. Their decompositions to produce mullite and silica are described and contrasted. The effect of nanomilling on those decompositions is discussed. Finally, the locations of commercial deposits and the industrial applications are addressed.The sillimanite minerals are the three anhydrous aluminosilicates: andalusite, kyanite, and sillimanite [1,2]. Kyanite is also referred to as cyanita, cyanite, and disthene. Because all three have the same 1:1 molar ratio of alumina (Al2O3) to silica (SiO2), they are often written simply as Al2O3·SiO2 or Al2SiO5. Their ideal composition is 62.92 wt% alumina and 37.08 wt% silica. However, in natural states involving significant impurities, the alumina content is usually less than 60 wt%. There are reports of higher alumina content deposits associated with the presence of higher alumina content minerals. That such a mineral group exists is not surprising, for the three most common elements in the Earth’s crust are O, Si, and Al.