The American Museum
of Natural History:
The Allison and Roberto Mignone
Hall of Minerals and Gems
BY LORRAINE BERTAN,
CULTURAL AFFAIRS
COMMITTEE
The Allison and Roberto
Mignone Hall of Minerals
and Gems at the American
Museum of Natural History has
all the drama of a stage produc-tion,
along with a narrative that
explains the role of the gorgeous
inanimate mineral characters which
seem to come alive in their setting.
Like plants and animals, minerals
evolve and their environment plays
a formative role in their evolution.
The earth has evolved from a mol-ten
mass into layers determined by
density. Plate tectonics affect how
minerals form. The environments
which influence the formation of
minerals are hydrothermal, meta-morphic,
igneous, pegmatite and
weathering. Minerals which form in
hydrothermal environments are dis-solved
in hot water and can travel
through fissures and veins in rocks
depositing precious metals like gold.
Minerals which crystallize slowly
in igneous structures will be quite
large and are known as pegmatites.
Pegmatites are the source of gem-stones
and other valuable minerals.
Heat and pressure affect the chem-ical
composition of minerals. The
New York State mineral is garnet and
is a result of intense heat and pres-sure
associated with mountain build-ing,
a metamorphic environment.
The schist formation in Central Park
contains garnets and the excavations
for the Manhattan subways yielded
garnets. An impressive garnet-bear-ing
rock, amphibolite, from Gore
Mountain is featured in the exhibit.
Weathering from wind, water, ice and
plant action breaks down rocks and
minerals. Weathering is considered a
destructive force compared to plate
tectonics which is a constructive
force.
The minerals that formed in the
early days of the planet are quite
different from the minerals which
formed after the introduction of
life. Approximately three billion
years ago, photosynthetic bacteria
appeared on the surface of the
oceans and introduced oxygen
into the oceans and atmosphere,
producing the vivid colors of min-erals.
Life on earth has produced
minerals which are unique to our
planet. Carrying out the theme of
evolution, minerals are grouped
into species to show how scientists
classify them and humans use them.
Minerals like salt and gypsum will
evaporate from surface water and
are known as evaporites. Minerals
have a definite chemical composi-tion
and will form crystals, which
have a unique structure. Rocks are
a mixture of minerals.
Visitors can touch the large topaz
crystal in the exhibit, along with
other examples of minerals. The
gemstones exemplify the beauty
of crystal structure, especially
the octahedron diamond, which
allows for total internal reflection
of light, unique to the brilliance of
the diamond. Mineral inclusions,
like rutile, are responsible for the
“star” in the Star of India sapphire,
the largest in the world (563 car-ats),
with stars on both sides of
the stone. Star sapphires and star
rubies are cut into cabochon shape,
rather than brilliant faceted cuts, to
emphasize the star and depth of
color. Sapphires and rubies have
the same chemical composition,
corundum, aluminum oxide, an
extremely hard substance used for
grinding.
Amethyst and Topaz exhibit at the Allison and Roberto Mignone New
Halls of Minerals and Gems at the American Museum of Natural
History
Amethysts are members of
the quartz family, with the same
chemical composition as sand and
glass, silicon dioxide, but contain
trace amounts of iron which pro-vides
the purple color. It is always
pleasurable to look at beautiful
jewelry, and knowing about the
science of minerals enhances the
experience. The beauty of nature
and the eye and hand of the artist
come together in this exhibit. The
jewels exhibited are from ateliers
like Cartier, Bulgari and Tiffany.
Jade, which contains the miner-als
jadeite or nephrite, is a result
of metamorphic processes. The
swirling patterns and inclusions in
jade stones reveal earth processes
like subduction and mountain
building, a type of time capsule. The
beauty of jade carving is the pres-ence
of various inclusions which
affect the color of the jade. Areas
of the world which are sources
of jade are Myanmar, Guatemala
and Australia. An interesting green
jade carving in the exhibit contains
malachite, a copper mineral. The
swirling pattern of the mineral is
prized for carvings and furnishings.
The Russian Czars used malachite
for table tops, vases, ceremonial
objects which are on display the
St. Petersburg Hermitage Museum.
Lapis, a royal blue mineral contain-ing
golden flecks of iron pyrites is
the source of ultramarine blue, so
precious that is was ground into
paint pigment for religious paintings.
Giant colorful amethyst geodes
and blue-green malachite and azur-ite
specimens welcome the visitor
in a brightly lit 11,000 square foot
hall with 25 foot ceilings. To really
appreciate the beauty, complexity
and the science explained in the
exhibit, watch the short video
near the entrance before you tour
the hall.
The Allison and Roberto
Mignone Hall of Minerals and
Gems is one of the permanent
exhibits at the museum. At present,
all visitors are required to be vacci-nated
against Covid-19 to enter the
premises. Please visit the museum’s
website, www.amnh.org, for more
information.
Mignone Hall of Minerals and
Gems
34 NORTH SHORE TOWERS COURIER ¢ October 2021
/www.amnh.org
/www.amnh.org
