[guide.chat] In Reply To: [guide.chat] gypsum used in food, dentists, art, craft etcetera
- From: vanessa <qwerty1234567a@xxxxxxxxx>
- To: "GUIDE CHAT" <guide.chat@xxxxxxxxxxxxx>
- Date: Sat, 9 Mar 2013 12:56:48 -0000
i'm going to try making glass from paper, too scared at moment, trying to face
fear by doing crazy things that frighten me stupid, i am like the mad scientist
doing new things in my art room.
vanessa.
-----Original Message-----
From: James Liddell - Email Address: james.liddell2@xxxxxxxxxxxxxxx
Sent On: 09/03/2013 11:12
Sent To: vanessa, GUIDE CHAT - Email Address: qwerty1234567a@xxxxxxxxx,
guide.chat@xxxxxxxxxxxxx
Subject: In Reply To: [guide.chat] gypsum used in food, dentists, art, craft
etcetera
Vanessa;
Putting my Egyptologist hat on, gypsum was also used in the embalming process
to create mummies, especially those of Late Period and Ptolemaic Period.
I'll take the hat of now.
Jim.
-----Original Message-----
From: vanessa - Email Address: qwerty1234567a@xxxxxxxxx
Sent On: 09/03/2013 10:45
Sent To: GUIDE CHAT - Email Address: guide.chat@xxxxxxxxxxxxx
Subject: [guide.chat] gypsum used in food, dentists, art, craft etcetera
Gypsum
From Wikipedia, the free encyclopedia
This article is about the mineral. For other uses, see Gypsum (disambiguation).
Gypsum
Fibrous gypsum selenite showing its translucent property.
General
Category Sulfate minerals
Formula
(repeating unit) CaSO4·2H2O
Strunz classification 07.CD.40
Crystal symmetry Monoclinic 2/m
Unit cell a = 5.679(5) Å, b = 15.202(14) Å, c = 6.522(6) Å; ß = 118.43°;
Z=4
Identification
Color Colorless to white; may be yellow, tan, blue, pink, brown, reddish
brown or gray due to impurities
Crystal habit Massive, flat. Elongated and generally prismatic crystals
Crystal system Monoclinic 2/m - Prismatic
Twinning Very common on {110}
Cleavage Perfect on {010}, distinct on {100}
Fracture Conchoidal on {100}, splintery parallel to [001]
Tenacity Flexible, inelastic.
Mohs scale hardness 1.5-2 (defining mineral for 2)
Luster Vitreous to silky, pearly, or waxy
Streak White
Diaphaneity Transparent to translucent
Specific gravity 2.31-2.33
Optical properties Biaxial (+)
Refractive index na = 1.519-1.521
nß = 1.522-1.523
n? = 1.529-1.530
Birefringence d = 0.010
Pleochroism None
2V angle 58°
Fusibility 5
Solubility Hot, dilute HCl
References [1][2][3]
Major varieties
Satin spar Pearly, fibrous masses
Selenite Transparent and bladed crystals
Alabaster Fine-grained, slightly colored
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate,
with the chemical formula CaSO4·2H2O.[3] It can be used as a fertilizer, is the
main constituent in many forms of plaster and is widely mined. As a mineral, it
is alabaster, which has been used for sculpture by many cultures including
Ancient Egypt, Mesopotamia and the Nottingham alabasters of medieval England.
It is the definition of a hardness of 2 on the Mohs scale of mineral hardness.
It forms as an evaporite mineral and as a hydration product of anhydrite.
The word gypsum is derived from the Greek word ????? (gypsos), "chalk" or
"plaster".[4] Because gypsum from the quarries of the Montmartre district of
Paris have long furnished burnt gypsum (calcined gypsum) used for various
purposes, this dehydrated gypsum became known as plaster of Paris. Upon
addition of water, after a few tens of minutes plaster of Paris becomes regular
gypsum (dihydrate) again, causing the material to harden or "set" in ways that
are useful for casting and construction.
Gypsum was known in Old English as spærstan, "spear stone", referring to its
crystalline projections. (Thus, the word spar in mineralogy is by way of
comparison to gypsum, referring to any non-ore mineral or crystal that forms in
spearlike projections.) Gypsum may act as a source of sulfur for plant growth,
and in the early 19th century, it was regarded as an almost miraculous
fertilizer. American farmers were so anxious to acquire it that a lively
smuggling trade with Nova Scotia evolved, resulting in the so-called "Plaster
War" of 1812.[5]
[edit]Physical properties
Gypsum is moderately water-soluble (~2.0-2.5 g/l at 25°C)[6] and, in contrast
to most other salts, it exhibits a retrograde solubility, becoming less soluble
at higher temperatures. When the crystal lattice is heated, it loses liquid
water molecules to evaporation and thus gains solidity. As for anhydrite, its
solubility in saline solutions and in brines is also strongly dependent on NaCl
concentration.[6]
Gypsum crystals are found to contain anion water and hydrogen bonding.[7]
[edit]Crystal varieties
Main article: Selenite (mineral)
Gypsum occurs in nature as flattened and often twinned crystals, and
transparent, cleavable masses called selenite. Selenite contains no significant
selenium; rather, both substances were named for the ancient Greek word for the
Moon.
Selenite may also occur in a silky, fibrous form, in which case it is commonly
called "satin spar". Finally, it may also be granular or quite compact. In
hand-sized samples, it can be anywhere from transparent to opaque. A very
fine-grained white or lightly tinted variety of gypsum, called alabaster, is
prized for ornamental work of various sorts. In arid areas, gypsum can occur in
a flower-like form, typically opaque, with embedded sand grains called desert
rose. It also forms some of the largest crystals found in nature, up to 12
metres (39 ft) long, in the form of selenite.[8]
[edit]Occurrence
Veins of gypsum in the silts/marls of the Tea Green and Grey Marls, Blue
Anchor, Somerset, UK.
Veins of gypsum in the Chugwater Group, Wyoming.
Gypsum is a common mineral, with thick and extensive evaporite beds in
association with sedimentary rocks. Deposits are known to occur in strata from
as far back as the Archaean eon.[9] Gypsum is deposited from lake and sea
water, as well as in hot springs, from volcanic vapors, and sulfate solutions
in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by
groundwater in near-surface exposures. It is often associated with the minerals
halite and sulfur. Pure gypsum is white, but other substances found as
impurities may give a wide range of colours to local deposits.
Because gypsum dissolves over time in water, gypsum is rarely found in the form
of sand. However, the unique conditions of the White Sands National Monument in
the US state of New Mexico have created a 710 km2 (270 sq mi) expanse of white
gypsum sand, enough to supply the construction industry with drywall for 1,000
years.[10] Commercial exploitation of the area, strongly opposed by area
residents, was permanently prevented in 1933 when president Herbert Hoover
declared the gypsum dunes a protected national monument.
Gypsum is also formed as a by-product of sulfide oxidation, amongst others by
pyrite oxidation, when the sulfuric acid generated reacts with calcium
carbonate. Its presence indicates oxidizing conditions. Under reducing
conditions, the sulfates it contains can be reduced back to sulfide by sulfate
reducing bacteria. Electric power stations burning coal with flue gas
desulfurization produce large quantities of gypsum as a byproduct from the
scrubbers.
Orbital pictures from the Mars Reconnaissance Orbiter (MRO) have indicated the
existence of gypsum dunes in the northern polar region of Mars,[11] which were
later confirmed at ground level by the Mars Exploration Rover (MER)
Opportunity.[12]
[edit]Mining
Golden gypsum crystals from Winnipeg.
Gypsum sand from White Sands National Monument, New Mexico.
Commercial quantities of gypsum are found in the cities of Araripina and
Grajaú, Brazil, Pakistan, Jamaica, Iran (world's second largest producer),
Thailand, Spain (the main producer in Europe), Germany, Italy, England,
Ireland, in British Columbia, Manitoba, Ontario,[13] Nova Scotia[14] and
Newfoundland in Canada,[15] and in New York, Michigan, Indiana,[15] Texas (in
the Palo Duro Canyon), Iowa, Kansas, Oklahoma, Arizona, New Mexico, Colorado,
Utah, Arkansas and Nevada in the United States. There is also a large open pit
quarry located at Plaster City, California, in Imperial County, and in East
Kutai, Kalimantan. Several small mines also exist in places such as Kalannie in
Western Australia, where gypsum is sold to private buyers for changing the pH
levels of soil for agricultural purposes.
Crystals of gypsum up to 11 meters (36 ft) long have been found in the caves of
the Naica Mine of Chihuahua, Mexico. The crystals thrived in the cave's
extremely rare and stable natural environment. Temperatures stayed at 58°C
(136°F), and the cave was filled with mineral-rich water that drove the
crystals' growth. The largest of those crystals weighs 55 short tons (50,000
kg) and is around 500,000 years old.[16]
[edit]Synthesis
Synthetic gypsum is recovered via flue-gas desulfurization at some coal-fired
power plants. It can be used interchangeably with natural gypsum in some
applications.
Gypsum also precipitates onto brackish water membranes, a phenomenon known as
mineral salt scaling, such as during brackish water desalination of water with
high concentrations of calcium and sulfate. Scaling decreases membrane life and
productivity. This is one of the main obstacles in brackish water membrane
desalination processes, such as reverse osmosis or nanofiltration. Other forms
of scaling, such as calcite scaling, depending on the water source, can also be
important considerations in distillation, as well as in heat exchangers, where
either the salt solubility or concentration can change rapidly.
A new study[17] has found the formation of gypsum starts as tiny crystals of a
mineral called bassanite (CaSO4.0.5H2O). This process occurs via a three-stage
pathway: (1) homogeneous nucleation of nanocrystalline bassanite; (2)
self-assembly of bassanite into aggregates, and (3) transformation of bassanite
into gypsum.
[edit]Uses of gypsum
Gypsum is used in a wide variety of applications:
Gypsum board[18] is primarily used as a finish for walls and ceilings, and is
known in construction as drywall or plasterboard.
Plaster ingredient (surgical splints, casting moulds, modeling)
Fertilizer and soil conditioner: In the late 18th and early 19th centuries,
Nova Scotia gypsum, often referred to as plaster, was a highly sought
fertilizer for wheat fields in the United States. It is also used in
ameliorating high sodium soils.[19]
A binder in fast-dry tennis court clay
As alabaster, a material for sculpture, especially in the ancient world before
steel was developed, when its relative softness made it much easier to carve
than stone with available tools.
A wood substitute in the ancient world: For example, when wood became scarce
due to deforestation on Bronze Age Crete, gypsum was employed in building
construction at locations where wood was previously used.[20]
A tofu (soy bean curd) coagulant, making it ultimately a major source of
dietary calcium, especially in Asian cultures which traditionally use few dairy
products
Adding hardness to water used for homebrewing[21]
Used in baking as a dough conditioner, reducing stickiness, and as a
baked-goods source of dietary calcium.[22] The primary component of mineral
yeast food.[23]
A component of Portland cement used to prevent flash setting of concrete
Soil/water potential monitoring (soil moisture tension)
A common ingredient in making mead
In the medieval period, it was mixed, by scribes and illuminators, with lead
carbonate (powdered white lead) to make gesso, which was applied to illuminated
letters and gilded with gold in illuminated manuscripts.
In foot creams, shampoos and many other hair products
A medicinal agent in traditional Chinese medicine called shi gao
Impression plasters in dentistry
from
Vanessa The Google Girl.
my skype name is rainbowstar123
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