Minerals in Sedimentary Systems II. Evaporates

Minerals in Sedimentary Systems II. Evaporates
Arabian Gulf
Panamint Valley
A California Salt Lake
California Desert Sands
Mediterranean Evaporates
Evaporate Deposits
Evaporate Minerals
Evaporite minerals from seawater
Halides, sulfates, carbonates,….while not here borates
are also important
Evaporite sequence
• From seawater, evaporite minerals tend to
form in a specific sequence
• Calcite
• Gypsum
• Halite
• Mg and K sulfates and chlorides
Evaporite sequence
•
•
•
•
•
Evaporate 1000 ft. of seawater to get
minor calcite
0.5 ft. of gypsum or anhydrite
11.8 ft. of halite
15 ft. Mg and K sulfates and chlorides including
NaCl
• Halite (NaCl) often forms 95% of the chloride
minerals
Halides
•
•
•
•
•
Defined by the dominance of Halogen ions
Cl-, Br-, F-, IStrongly ionic
Halite, sylvite common evaporates
In halite, individual molecules do not exist
instead a single crystal lattice is present
• Fluorite (CaF2) is also a halide, but not an
evaporite
Halite NaCl
Basic use is nutrition and
the preservation of food.
The term salary comes from
the Latin word for salt.
Roman soldiers were paid in
pounds of salt, and hence
the term, “not worth his or
her salt”.
A halide mineral, isometric, cubic crystals
Trona
Trona Halides
Trona Halite
Trona
Salt Dome
Structure
Bedded halite ductilely flows
under the great pressures of
deep burial. And, due to its
low density, halite rises as
diapirs from its deep layers to
form salt domes.
Truncated layers punctured
by the rising salt form perfect
oil traps, which like the salt is
also rising upward.
Gulf Coast Salt Domes
Iran Salt Domes and Anticlines
Iran Salt Domes and Anticlines
Salt Dome
Trona Pinnacles
Tufa mounds are made of
aragonite or calcite precipitated
around underwater springs at the
base of lakes.
Trona Pinnacle Carbonate - Tufa
Borax
Borates
• Over 135 known borate minerals; 4 are
most common.
• Kernite- Na2B4O6(OH)2*3H2O
• Borax- Na2B4O5(OH)4*8H2O
• Ulexite- NaCaB5O6(OH)6*5H2O
• Colemanite- CaB3O4(OH)3*H2O
Borax - an Evaporate Mineral
Na2B4O5(OH)4 8H2 O
Approx. Density : 1.715
Related minerals include colemanite, kernite, and ulexite
Borax
Well over a century ago borates – usually the disodium tetraborate decahydrate salt (borax
decahydrate*, Na2B4O7.10H2O) - became popular wash-day additives. They were famed,
once they became easily and cheaply available, for their gentle but strong cleaning action.
Ulexite
It’s gypsum, var.satin spar
Ulexite (NaCaB5O6(OH)6 . 5 H2O) is a borate mineral famous for its unusual optical
properties; it's named for its discoverer, the German chemist G. L. Ulex.
Sulfates
Gypsum
CaSO4-2(H2O)
Gypsum
a commom sedimentary mineral
CaSO4-2(H2O)
Uses: plaster, wall board, some cements, fertilizer, paint
filler, ornamental stone, etc..
Gypsum is one of the more common minerals in
sedimentary environments. It is a major rock forming
mineral that produces massive beds, usually from
precipitation out of highly saline waters.
Gypsum
Gypsum - a Closer View
Varieties of Gypsum
Gypsum has several variety names that are widely used in the
mineral trade.
*
"Selenite" is the colorless and transparent variety that
shows a pearl like luster and has been described as having a moon
like glow. The word selenite comes from the greek for Moon and
means moon rock.
*
Another variety is a compact fiberous aggregate called
"satin spar" . This variety has a very satin like look that gives a
play of light up and down the fiberous crystals.
*
A fine grained massive material is called "alabaster" and is
an ornamental stone used in fine carvings for centuries, even eons.
Anhydrite
Anhydrite does not form
directly, but is the result of
the dewatering of the rock
forming mineral Gypsum
(CaSO4-2H2O). This loss of
water produces a reduction
in volume of the rock layer
and can cause the
formation of caverns as the
rock shrinks.
Anhydrite
Phosphates
Apatite
Apatite
The apatite group is
composed of minerals
of the general formula
Ca5(PO4)3(OH,F,Cl).
Apatite occurs as a finegrained sedimentary rock
called phosphorite as a
direct precipitate from sea
water. It is also an accessory
mineral in many igneous
rocks. Miocene Shark’s Tooth
Apatite Structure
Apatite - a Different View
The main producers of phosphate rock
and phosphate fertilizers are the USA,
the former USSR, China, Africa (the
Maghreb countries, Egypt, Senegal,
Togo and South Africa), and the Middle
East. Several of these countries are
developing countries and the phosphate
industry makes an important
contribution to their economies. More
than 75% of the world's commercially
exploited phosphate rock is surface
mined.
Overall, mineral fertilizers account for
approximately 80% of phosphate use,
with the balance divided between
detergents (12%), animal feeds (5%)
and specialty applications (3%), e.g.
food grade, metal treatment etc.
Apatite
Phosphorite
Outcrop
Phosphate rock is formed in oceans
in the form of calcium phosphate,
called phosphorite. It is deposited in
extensive layers that cover
thousands of square miles.
In the oceans the phosphorus is
precipitated by organisms and
sometimes by chemical reaction.
The most important use of
phosphate rock is in the production
of phosphate fertilizers for
agriculture.
Phosphorite Nodules
Microscope View of Phosphorite
Phosphorus in Sea Water, South Florida
Fertilizer Phosphates and
evaporites
Barite Rose
a concretion of sandstone with barite cement
Barite Structure BaSO4
Barite Mine
Follow the vein
Barite Production World Wide
1930 Mining of Barite - Arkansas
Barite
Barite (BaSO4), the only
commercial source of barium and
barium compounds, is a relatively
soft, inert mineral with a high SG
(Specific Gravity) in the range of
4.2-4.5.
Approximately 90% of world
production is used as a weighting
agent in drilling mud for oil and
gas wells where the high SG
assists in containing pressures and
preventing blowouts.
Barite
Barite is used as a heavy filler in
special paper, rubber, paint and
plastics.
Its radiation absorbing properties
are used in special concretes and in
barium meals for medical X-ray
examinations.
Barium compounds are used in
ceramic glazes and to enhance the
brilliance and clarity of optical and
TV glass.