Smithsonite Composition, Crystallization & Structure

Composition. Zinc carbonate, ZnCO₃ = Carbon dioxide 32.2, zinc protoxide 64.8 Iron and manganese often replace a part of the zinc; also a t times calcium and magnesium.

Crystallization. Hexagonal-rhombohedral. Rarely in small rhombohedral or scalenohedral crystals.

Structure. Usually reniform, botryoidal or stalactitic and in crystalline incrustations or in honeycombed masses known as dry-bone ore. Also granular to earthy. Distinct crystals rare.

Physical Properties. Perfect rhombohedral cleavage, which, on account of the usual structure, is seldom observed. H. = 5 (unusually high for a carbonate). G. = 4.30-4.35. Vitreous luster. Color usually dirty brown. May be white, green, blue, pink, etc. Translucent to opaque.

Tests. Infusible. Soluble in hydrochloric acid with effervescence. A fragment heated B.B. in R. F. gives bluish green streaks in the flame, due to the burning of the volatilized zinc. Heated in R. F. on charcoal gives a nonvolatile coating of zinc oxide yellow when hot, white when cold; if coating is moistened with cobalt nitrate and again heated it turns green. Distinguished by its effervescence in acids, its tests for zinc, its hardness (5) and its high specific gravity.

Occurrence. It is a zinc ore of secondary origin. Found in connection with zinc deposits near the surface, and where the oxidized ores have been acted upon carbonated waters. Common in connection with zinc deposits lying in limestone rocks. Associated with sphalerite, galena, calamine, cerussite, calcite, limonite, etc.  Often found in pseudomorphs after calcite “Dry-bone ore” is a honeycombed mass, with the appearance of dried bone, whose structure has resulted from the manner of deposition of the mineral. Some calamine, the silicate of zinc, is included under the term. Occurs, as an ore, in the zinc deposits of Missouri, Arkansas, Wisconsin, Virginia, etc. Found at times in translucent green or greenish blue material which is available for ornamental uses. Such smithsonite is found at Laurium, Greece, and at Kelly, New Mexico. In yellow stalactites with banded structure from Sardinia.

Name. Named in honor of James Smithson (1754 – 1829), who founded the Smithsonian Institution at Washington. English mineralogists call the mineral calamine, using either electric calamine or hemimorphite as the name for the silicate.

Use. An ore of zinc.