magnesia See magnesium oxide.
magnesite A white, colourless, or
grey mineral form of *magnesium
carbonate, MgCO 3 , crystallizing in
the trigonal system. It is formed as a
replacement mineral of magnesiumrich rocks when carbon dioxide is
available. Magnesite is mined both as
an ore for magnesium and as a
source of magnesium carbonate. It
occurs in Austria, USA, Greece, Norway, India, Australia, and South
Africa.
magnesium Symbol Mg. A silvery
metallic element belonging to group
2 (formerly IIA) of the periodic table
(see alkaline-earth metals); a.n. 12;
r.a.m. 24.305; r.d. 1.74; m.p. 648.8°C;
b.p. 1090°C. The element is found in
a number of minerals, including
magnesite (MgCO 3 ), dolomite
(MgCO 3 .CaCO 3 ), and carnallite
(MgCl 2 .KCl.6H 2 O). It is also present in
sea water, and it is an *essential element for living organisms. Extraction is by electrolysis of the fused
chloride. The element is used in a
number of light alloys (e.g. for aircraft). Chemically, it is very reactive.
In air it forms a protective oxide coating but when ignited it burns with
an intense white Ûame. It also reacts
with the halogens, sulphur, and nitrogen. Magnesium was Ürst isolated
by Bussy in 1828.
A
• Information from the WebElements site
magnesium bicarbonate See
magnesium hydrogencarbonate.
magnesium carbonate A white
compound, MgCO 3 , existing in anhydrous and hydrated forms. The anhydrous material (trigonal; r.d.
2.96) is found in the mineral *magnesite. There is also a trihydrate,
MgCO 3 .3H 2 O (rhombic; r.d. 1.85),
which occurs naturally as nesquehonite, and a pentahydrate,
MgCO 3 .5H 2 O (monoclinic; r.d. 1.73),
which occurs as lansfordite. Magnesium carbonate also occurs in the
mixed salt *dolomite (CaCO 3 .MgCO 3 )
and as basic magnesium carbonate in the two minerals artinite
(MgCO 3 .Mg(OH) 2 .3H 2 O) and hydromagnesite (3MgCO 3 .Mg(OH) 2 .3H 2 O).
The anhydrous salt can be formed by
heating magnesium oxide in a
stream of carbon dioxide:
MgO(s) + CO 2 (g) → MgCO 3 (s)
Above 350°C, the reverse reaction
predominates and the carbonate decomposes. Magnesium carbonate is
used in making magnesium oxide
and is a drying agent (e.g. in table
salt). It is also used as a medical
antacid and laxative (the basic carbonate is used) and is a component
of certain inks and glasses.
magnesium chloride A white
solid compound, MgCl 2 . The anhydrous salt (hexagonal; r.d. 2.32; m.p.
714°C; b.p. 1412°C) can be prepared
by the direct combination of dry
chlorine with magnesium:
Mg(s) + Cl 2 (g) → MgCl 2 (s)
The compound also occurs naturally
as a constituent of carnallite
(KCl.MgCl 2 ). It is a deliquescent compound that commonly forms the
hexahydrate, MgCl 2 .6H 2 O (monoclinic; r.d. 1.57). When heated, this
hydrolyses to give magnesium oxide
and hydrogen chloride gas. The fused
chloride is electrolysed to produce
magnesium and it is also used for
ÜreprooÜng wood, in magnesia cements and artiÜcial leather, and as a
laxative.
magnesium hydrogencarbonate
(magnesium bicarbonate) A compound, Mg(HCO 3 ) 2 , that is stable only
in solution. It is formed by the action
of carbon dioxide on a suspension of
magnesium carbonate in water:
magnesia
336
m
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magnesite A white, colourless, or
grey mineral form of *magnesium
carbonate, MgCO 3 , crystallizing in
the trigonal system. It is formed as a
replacement mineral of magnesiumrich rocks when carbon dioxide is
available. Magnesite is mined both as
an ore for magnesium and as a
source of magnesium carbonate. It
occurs in Austria, USA, Greece, Norway, India, Australia, and South
Africa.
magnesium Symbol Mg. A silvery
metallic element belonging to group
2 (formerly IIA) of the periodic table
(see alkaline-earth metals); a.n. 12;
r.a.m. 24.305; r.d. 1.74; m.p. 648.8°C;
b.p. 1090°C. The element is found in
a number of minerals, including
magnesite (MgCO 3 ), dolomite
(MgCO 3 .CaCO 3 ), and carnallite
(MgCl 2 .KCl.6H 2 O). It is also present in
sea water, and it is an *essential element for living organisms. Extraction is by electrolysis of the fused
chloride. The element is used in a
number of light alloys (e.g. for aircraft). Chemically, it is very reactive.
In air it forms a protective oxide coating but when ignited it burns with
an intense white Ûame. It also reacts
with the halogens, sulphur, and nitrogen. Magnesium was Ürst isolated
by Bussy in 1828.
A
• Information from the WebElements site
magnesium bicarbonate See
magnesium hydrogencarbonate.
magnesium carbonate A white
compound, MgCO 3 , existing in anhydrous and hydrated forms. The anhydrous material (trigonal; r.d.
2.96) is found in the mineral *magnesite. There is also a trihydrate,
MgCO 3 .3H 2 O (rhombic; r.d. 1.85),
which occurs naturally as nesquehonite, and a pentahydrate,
MgCO 3 .5H 2 O (monoclinic; r.d. 1.73),
which occurs as lansfordite. Magnesium carbonate also occurs in the
mixed salt *dolomite (CaCO 3 .MgCO 3 )
and as basic magnesium carbonate in the two minerals artinite
(MgCO 3 .Mg(OH) 2 .3H 2 O) and hydromagnesite (3MgCO 3 .Mg(OH) 2 .3H 2 O).
The anhydrous salt can be formed by
heating magnesium oxide in a
stream of carbon dioxide:
MgO(s) + CO 2 (g) → MgCO 3 (s)
Above 350°C, the reverse reaction
predominates and the carbonate decomposes. Magnesium carbonate is
used in making magnesium oxide
and is a drying agent (e.g. in table
salt). It is also used as a medical
antacid and laxative (the basic carbonate is used) and is a component
of certain inks and glasses.
magnesium chloride A white
solid compound, MgCl 2 . The anhydrous salt (hexagonal; r.d. 2.32; m.p.
714°C; b.p. 1412°C) can be prepared
by the direct combination of dry
chlorine with magnesium:
Mg(s) + Cl 2 (g) → MgCl 2 (s)
The compound also occurs naturally
as a constituent of carnallite
(KCl.MgCl 2 ). It is a deliquescent compound that commonly forms the
hexahydrate, MgCl 2 .6H 2 O (monoclinic; r.d. 1.57). When heated, this
hydrolyses to give magnesium oxide
and hydrogen chloride gas. The fused
chloride is electrolysed to produce
magnesium and it is also used for
ÜreprooÜng wood, in magnesia cements and artiÜcial leather, and as a
laxative.
magnesium hydrogencarbonate
(magnesium bicarbonate) A compound, Mg(HCO 3 ) 2 , that is stable only
in solution. It is formed by the action
of carbon dioxide on a suspension of
magnesium carbonate in water:
magnesia
336
m
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