Lithosphere

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Lithosphere vs Asthenosphere
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Plate Motion
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Plate Tectonics and Rock Cycle
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Geological Processes for Gemstones Formation
Magmatic mineral deposits concentrated in igneous
rocks Hydrothermal/Pegmatitic mineral deposits
form in association with hot water- or gas-rich
fluids Metamoprhogenic mineral deposits
concentrated by metamorhism / metasomatism Sedimen
tary mineral deposits are precipitated from a
solution, typically sea water Placer minerals
are sorted and distributed by flow of water (or
ice) Residual mineral deposits formed by
weathering reactions at the earth's
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Schematic model of a fully grown kimberlite pipe
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Pegmatite
Pegmatite
Gneiss
Gneiss
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Gem-bearing Pegmatites
Pegmatite is often found in veins (dikes)
penetrating into surrounding continental country
rock, although it can exist as very large bodies
also (stock or batholith size). As with all
felsic rocks, is found on continents. It is one
of the last fractionation products and typically
results from partial melting of the lower crust.
http//geollab.jmu.edu/Fichter/IgnRx/GranAlk4B1.ht
ml
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Pegmatite containing tourmaline
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Cassedanne, J.P. and Roditi. M., 1996. The
location, geology and mineralogy of gem
tourmalines in Brazil. Journal of Gemmology,
Volume 25, No. 4, pp. 263-298.
Tourmaline-bearing pegmatites, which commonly are
lens-shaped, are variable in their strike and
dip, and show a range of patterns of zoning and
albitization. Wallrocks are mica schists,
quartzites or rarely granite or gneiss, all
Precambrian in age. The pegmatites occur either
singly or in fields or clusters and belong to the
Brazilian tectonic cycle (650-450 m.y.). Five
types of gem-bearing pegmatites are described
1) poorly differentiated, almost homogeneous,
with small albitic replacement bodies 2)
poorly differentiated with strong albitization
3) zoned with small albitic replacement bodies
4) zoned with strong albitization 5)
lithium-rich, very well zoned, with strong
albitization.
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Spessartite in pegmatite matrix http//www.mineral
miners.com/html/spemins.stm
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This photograph shows giant lithium crystals of
the mineral spodumene in a pegmatite in the Black
Hills of South Dakota. http//www.science.uwaterlo
o.ca/earth/geoscience/pegmat.html
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Spodumene From the Greek, spodoumenos, meaning
"burnt to ash".
Spodumene forms as flattened, prism-shaped
crystals that can be very large, up to 16 meters
long and weighing several tons. The crystals have
fine, vertical ridges (striations). Spodumene
can be colored white, gray, yellowish, green
(hiddenite), and pink to purple (kunzite).
http//www.sdnhm.org/fieldguide/minerals /spodume
ne.html
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Spodumene are an important source of lithium.
Hiddenite and kunzite are used as gemstones even
though spodumene cracks easily. It is found only
in granite pegmatites. It can be found in
Scotland, Sweden, Brazil, Burma, and parts of
North America. Kunzite, the pale pink to lilac
gem variety of the mineral spodumene, is named as
a tribute to George Kunz, the legendary gem
scholar, gemologist, and gem buyer. It is often
found in association with morganite and pink
tourmaline, the other popular pink gemstones.
Today most kunzite is mined in Brazil,
Afghanistan, and Madagascar. Hiddenite is the
green variety of spodumene. It is an attractive
gem mineral, but is rare and for the most part
known only to collectors.
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Gemstones in Volcanic Rocks
Peridot in Vesicular Basalt
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Hydrothermal Gemstone
Colombian Beryl Deposits
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Gemstones as Products of Weathering
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Origin of Gem Gravels
Gemstones in dikes or veins
Underwater potholes
Channel bed rifles
Point Bar
Water Fall
Tributary
Beach Placer
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Placer Gem Deposits
NAMIBIA
NAMIBIA
COLOMBIA
VIETNAM
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METAMORPHIC GEMSTONE JADEITE
Jadeite - is a sodium aluminum pyroxene that is
characterized by its presence in metamorphic
rocks formed at relatively high pressure. It can
form by a reaction of Albite to produce
NaAlSi3O8 NaAlSi2O6 SiO2 Albite
Jadeite Quartz
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JET JEWELLERY
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(Malm)
(Dogger)
(Lias)
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http//www.whitbyjet.co.uk/aboutjet.html
Monkey-puzzle tree or Chilean pine
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Amber the Jurassic Gem
Millions of people learned from the movie that
amber, which is fossilized pine tree sap, is
ancient and valuable, like an antique from
previous history. The two main sources of amber
on the market today are the Baltic states and the
Dominican Republic. Amber from the Baltic states
is older, and therefore preferred on the market,
but amber from the Dominican Republic is more
likely to have insect inclusions. Prices of amber
can range from 20 to 40,000 or more.
www.gemstone.org
The amber, which was from the Lower Cretaceous
period, was mined in the mountains of Lebanon
south of Beirut by Aftim Acra, who has a
collection of amber pieces containing 700
insects, including termites, moths, caterpillars,
spiders, pseudoscorpions, and midges, which do
suck blood.
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Lapis Lazuli
Lapis Lazuli is a rock composed chiefly of the
blue silicate mineral lazurite, together with
calcite and brassy-coloured pyrite which are
abundant in the poorer quality material. The
vivid blue of lazurite is cause by the sulphur
that forms an essential part of its chemistry.
Today lapis lazuli is also mined in Siberia and
in Chile, but material from these sources usually
contains much calcite.
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• Lapis Lazuli is normally a mixture of three
  minerals
• lazurite (Na,Ca)8 (AlSiO4 )6 (S,SO4 ,Cl)1-2
• calcite (calcium carbonate, which is white)
• pyrite (an iron sulfide that is white-gold in
  color)
• Lapis lazuli, is a contact metamorphic rock with
  variable composition and varying physical
  properties. It usually forms by contact
  metamorphism of limestones.

Lazurite is a felspathoid (somewhat
feldspar-like) cubic (thus, isotropic) hardness
5.5 S.G. 2.7 - 2.9 vitreous / greasy luster.
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For many centuries the only known deposits were
those at Sar-i-Sang, in a remote mountain valley
in Badakhshan, Afghanistan. At Sar-i-Sang the
lapis lazuli occurs as a zone of lenses and veins
within white marble, and grades from deep to pale
blue with some violet and greenish tints. From
here it was exported to the ancient civilizations
of Egypt and Sumer (Ira), and later traded
throughout the East and into Europe. These mines
are still producing the finest quality lapis
lazuli.
1 cm..
Lazurite crystal in quartz matrix