Gems in the Smithsonian InstitutionDesautels, Paul E.
History
Gems in the Smithsonian Institution
Desautels, Paul E.
Gems; Precious stones; Smithsonian Institution
Although spessartine has a rich orange color, it is not often used as a
gemstone because of the relative rarity of gem-quality cutting material.
This mineral gets its name from the town of Spessart, Germany, where it
was first found. Excellent spessartine with colors ranging from orange
to brown has been found at Amelia Court House, Va., and quality gems
have been cut from such material. Ceylon, Burma, Madagascar, and Brazil
also have furnished some gem spessartine.
The chromium garnet, uvarovite, generally is too poor in quality for
cutting. Uvarovite crystals, which are emerald green in color, occur in
only small sizes. They are found mostly in Russia, Finland, and
California.
Grossular varies in color. It occurs chiefly in some shade of red,
green, yellow, or brown, depending on the impurities present. When pure,
grossular is colorless. A kind of grossular called _hessonite_ has an
attractive cinnamon color, and it is found mainly in Ceylon. Because of
its color it can easily be confused with spessartine, which it closely
resembles.
Andradite, a very common garnet, usually is found in shades of red,
black, brown, yellow, or green. Some types of gem andradite have special
names for different colors: _topazolite_, yellow; _demantoid_, green;
and _melanite_, sparkling black. The very valuable demantoid is found in
Russia and Italy.
VARIETIES:
Grossular: Colorless, green, amber, brownish yellow, rose
Hessonite: Cinnamon colored
Pyrope: Deep red
Rhodolite: Rose red and purple
Almandine: Deep red
Spessartine: Brownish red to orange
Andradite: Yellow, greenish yellow, emerald green, brownish red,
brownish yellow, brown, black
Topazolite: Yellow to greenish
Demantoid: Grass green to emerald green
Melanite: Black
Uvarovite: Green
JADE
The name jade is applied to two unrelated minerals—_nephrite_ and
_jadeite_—that have somewhat similar characteristics.
Jadeite, the rarer of the two, is a sodium aluminum silicate that
belongs to a group of rock-forming minerals known as pyroxenes. Its
color varies from white to emerald green and many other colors. Jadeite
is highly prized, and when it occurs as emerald green it is considered
one of the most valuable gemstones. This kind of jade is found in many
places, but the most important occurrence is in Upper Burma. Nephrite, a
more common species, is a calcium magnesium iron silicate belonging to a
group of rock-forming minerals known as amphiboles. The color varies
from white to a dark spinach green and black. Among the places where
nephrite occurs are New Zealand, Turkestan, Siberia, Alaska, China,
Silesia, and certain parts of the western United States, notably in
Wyoming and California.
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