Jeweller - July, Edition I 2020

REVIEW
Gems
The green fire of Peridot
L to R: Peridot rough; peridot and diamond collier, Sotheby’s;
Dreamcatcher peridot earrings, Temple St Clair
Forming deep within the Earth’s mantle,
peridot is no stranger to heat and pressure.
This green mineral may also be of extraterrestrial
origin, transported within
meteorites from the depths of the universe,
impacting the Earth in rare, cataclysmic
events.
Peridot is a member of the olivine group of
minerals that form an isomorphous series
of magnesium-iron silicates. The two endmembers
of the series are the magnesiumrich
forsterite and the iron-rich fayalite.
Peridot is the gem-quality variety of olivine
and its colour ranges from green, greenishyellow,
yellowish-green, greenish-brown
and brown, depending on its chemical
composition.
Pure green gemstones are rare and most
peridot exhibits a yellowish undertone.
The intensity of peridot’s green hue is
determined by the varying amount of iron in
its composition; iron influences a yellowbrown
tone within the gemstone while
traces of chromium and nickel – replacing
iron and magnesium – are said to give
peridot a bright-green colour.
Pallasite meteorites have expanded the
horizons of the study of peridot to the far
reaches of the galaxy.
Pallasites are one kind of stony-iron
meteorite that contain abundant crystalline
olivine, sometimes of gem-quality peridot.
“Mining is said to have begun around 300bc,
indicating that Cleopatra’s famous emerald
collection may in fact have been peridot.”
The crystals are generally small and, due
to the high iron content of the surrounding
iron-nickel matrix, are typically yellowybrown
in colour.
Some pallasitic peridot specimens are
higher in carat weight and present an
attractive green colour favourable for
faceted gemstones.
Pallasitic peridot usually contains
characteristic inclusions that separate it
from terrestrial peridot but the origin of
clean gemstones may require chemical
analysis.
Affordable and beautiful, peridot can be free
of eye-visible inclusions, particularly those
in smaller calibrated sizes.
Prices rise for gemstones greater than
10mm, particularly those with vivid-green
colour. Although larger gemstones can
present a high clarity, small and black
chromite crystals are characteristic of
Earth-formed peridot as are reflective, discshaped
‘lily-pad’ inclusions.
Gemstones that are lighter and less
intense in colour see a dramatic drop in
value regardless of their size, as do those
that present eye-visible inclusions. The
finest examples of peridot are unearthed
in Myanmar and Pakistan with Arizona and
Peridot
Origin uncertain,
believed to be Anglo-
Norman pedoretes
Colour: Pure green to
yellowish green
Found in: China,
Myanmar, Pakistan,
Tanzania, Vietnam,
United States
Mohs Hardness: 6.5–7
Class: Silicate
Lustre: Vitreous
Formula: Mg 2
SiO 4
China producing more reliable commercial
quantities.
Admired since the dawn of civilisation, early
records indicate the Ancient Egyptians
mined a beautiful green gemstone from the
island in the Red Sea called Topazios.
The island, now known as St John’s Island,
or Zabargad, remains to this day the oldest
and longest-known source of gem-quality
peridot.
Mining is said to have begun around 300BC,
indicating that Cleopatra’s famous emerald
collection may in fact have been peridot!
A gemstone always associated with light,
the Egyptians called peridot the “gem of the
sun”, believing it to protect its owner from
“terrors of the night”.
Fashioned into a variety of shapes and cuts,
faceted gemstones show a doubling of the
back facets – an optical property caused by
high birefringence and a diagnostic feature
of peridot.
Carvings, beads and cabochons are also
not uncommon although these forms don’t
capture peridot’s dispersive nature.
Now the most beautiful samples of peridot
come from the border area between
Pakistan and Afghanistan and the gemstone
is also found in Myanmar, China, the US,
Africa, Australia and Vietnam.
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