Leucite (English spelling)

Japanese: リューサイト（英語表記）leucite

Also called white sclerotin. Chemical composition KAlSi ₂ O ₆ , a mineral classified as a feldspar. The transition point is about 605°C, with the high-temperature type being isometric and the low-temperature type being tetragonal (pseudo-isometric). It usually occurs as an idiomorphic crystal of {211} rhombohedron, but this is the shape of the high-temperature type at the time of crystallization. At room temperature, it always transitions to the low-temperature type, and shows agglomerate twins under a microscope. White to gray, transparent crystals are rare. Cleavage {110}, shell-like, Mohs hardness 5.5-6, specific gravity 2.5, refractive index 1.508-1.509, very weak birefringence.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

白リュウ(榴)石ともいう。化学組成KAlSi₂O₆，準長石類に分類される鉱物。約605℃を転移点に高温型は等軸，低温型は正方晶系(偽等軸晶系)。ふつう｛211｝の偏菱二十四面体の自形結晶として産出するが，これは晶出時の高温型の外形を残したもので，常温では常に低温型に転移，鏡下で集片双晶を示す。白～灰色，透明結晶はまれ。へき開｛110｝，断口貝殻状，モース硬度5.5～6，比重2.5，屈折率1.508～1.509，複屈折は非常に弱い。

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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