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smithsonite (calamine) Mineral, ZnCO3; sp, gr. 4.4; hardness 4.5; trigonal; colour variable, shades of grey, brown, or greyish-white, but green, brown, and yellow types also occur; grey streak; vitreous lustre; crystals rare, but when they develop rhombohedral with curved faces, more usually occurs as botryoidal and stalactitic masses; cleavage perfect rhombohedral; occurs in the oxidized zone of zinc ore deposits, commonly associated with sphalerite, galena, and calcite, also as a replacement in limestone, and in hydrothermal veins; soluble in dilute hydrochloric acid, with effervescence. The green variety is used to make ornaments. It is named after the British mineralogist James Smithson (founder of the Smithsonian Institution in Washington, DC).