This
mineral, named after James Smithson, who founded the Smithsonian
Institution in Washington, is a carbonate of zinc used chiefly as an
ore of that metal. It is usually of a dull, earthy character and poorly
fitted for ornamental purposes. In some occurrences, however, it
exhibits pleasing colors and a translucency reminding one of onyx. When
so occurring it may be cut into ring stones, or even vases and other
dishes of considerable size and beauty. The smithsonite from Laurium,
Greece, is that perhaps most extensively used in this way, its color
usually being some shade of blue. From Siberia a beautiful bright green
smithsonite is obtained, the green color being due probably to a little
admixed copper, and from the zinc mines of Arkansas and Missouri a
bright yellow form is derived, known locally as "turkey fat ore." The
yellow color here is due to a little cadmium. All of these forms of
smithsonite exhibit when polished a rich luster and subtransparency
which are pleasing. The hardness of the mineral is somewhat deficient
for enduring wear, this being but 5. It is rather heavy, its specific
gravity being 4.3 to 4.4. It is infusible, but soluble in hydrochloric
acid with effervescence. When heated before the blowpipe a coating is
formed, which is yellow when hot and white on cooling. These tests
serve to distinguish the mineral from any others with which it might be
confounded.
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