calcium carbonate

名词 calcium carbonate:

1. a salt found in nature as chalk or calcite or aragonite or limestone

1. A smooth, lustrous, variously colored deposit, chiefly calcium carbonate, formed around a grain of sand or other foreign matter in the shells of certain mollusks and valued as a gem.
   珍珠在几种软体动物的贝壳中，围绕着一粒沙子或其他外来物质形成的一种光滑、有色泽、具有不同颜色且主要是碳酸钙的沉积物，被珍视为宝石