Sillimanite (English spelling)

Japanese: ケイ線石(珪線石) - けいせんせき（英語表記）sillimanite

Its chemical composition is Al ₂ SiO ₅ . It is an orthorhombic crystal mineral that forms fibrous or columnar crystals elongated along the c- axis. It is white to yellowish or greenish white in color and has a vitreous or silky luster. Its specific gravity is 3.25 and its Mohs hardness is 7.5. It is completely cleaved along {010}. It is in a polymorphic relationship with andalusite and cyanotype. Its stable region is higher in temperature and pressure than andalusite and higher in pressure than cyanotype, and it is commonly found as a rock-forming mineral in high-grade metamorphic rocks of pelitic origin. In Japan, it is often found in gneiss in the Ryoke metamorphic belt.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

化学組成はAl₂SiO₅。斜方晶系に属し，c軸に伸長した繊維状あるいは柱状結晶をなす鉱物。白色～帯黄ないし帯緑白色を呈し，ガラス光沢，絹糸光沢をもつ。比重3.25，モース硬度7.5。｛010｝にへき開が完全。紅柱石，ラン晶石と多形の関係にある。紅柱石よりも高温高圧側に，ラン晶石よりも高圧側に安定領域をもち，泥質岩起源の高度変成岩の造岩鉱物として普通に産出する。日本では領家変成帯の片麻岩によく見いだされる。

出典　株式会社平凡社世界大百科事典第２版について　情報

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