Aragonite

Japanese: アラゴナイト（英語表記）aragonite

Also called aragonite. Its chemical composition is CaCO ₃ , and it is a polymorphous mineral with calcite. It occurs as direct deposits from seawater, around hot springs, in limestone caves, in volcanic rock crystals, in the oxidation zones of mineral deposits, in sediments near the earth's surface, and in metamorphic rocks. It has an orthorhombic crystal system, single crystals are rare, and it often shows columnar or needle-like shapes, or pseudohexagonal shapes as a result of twinning. It forms various aggregates. It has a Mohs hardness of 3.5 to 4, a specific gravity of 2.947, and a clear cleavage in {010}. It is colorless to white, often showing various shades. It is the main component mineral of shells, pearls, corals, etc.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

アラレ(霰)石ともいう。化学成分はCaCO₃で方解石と多形をなす鉱物。海水からの直接沈殿物，温泉のまわりや石灰岩洞窟中，火山岩の晶洞，鉱床の酸化帯，地表近くの堆積物中に，また変成岩中にも産する。斜方晶系，単結晶はまれで，柱状ないし針状，双晶の結果，偽六方の外形をよく示す。種々の集合体をなす。モース硬度3.5～4，比重2.947，へき開は｛010｝に明瞭，無色ないし白色，しばしば各種の色調を示す。貝殻，真珠，サンゴなどの主要な構成鉱物である。

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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