Geoscience Reference
In-Depth Information
Table 4.2
Chemistry of various potassium, uranium and thorium minerals.
Mineral
Formula
Wt% K
Wt% U
Wt% Th
Feldpars
Orthoclase
KAlSi
3
O
8
14.05
Microcline
KAlSi
3
O
8
14.05
Sanidine
(K,Na)(Si,Al)
4
O
8
10.69
Anorthoclase
(Na,K)AlSi
3
O
8
3.67
Micas
K(Mg,Fe
2+
)
3
[AlSi
3
]O
10
(OH,F)
2
Biotite
9.02
Muscovite
KAl
2
(AlSi
3
)O
10
(OH,F)
2
9.81
Phlogopite
KMg
3
(AlSi
3
)O
10
(F,OH)
2
9.33
K(Fe
3+
,Al)
2
(Si,Al)
4
O
10
(OH)
2
Glauconite
5.49
Clay minerals
Illite
K
y
Al
4
(Si
8-y
Al
y
)O
20
(OH)
2
6.03
Evaporites
Sylvite
KCl
52.45
Carnallite
KMgCl
3
6H
2
O
14.07
U and Th minerals
Brannerite
(U,Ca,Ce)(Ti,Fe)
2
O
2
33.54
Carnotite
K
2
(UO
2
)
2
(VO
4
)
2
1
-
3H
2
O
8.67
52.77
Cof
nite
U(SiO
4
)
1-x
(OH)
4x
72.63
Monazite
(Ce,La,Nd,Th,Y)PO
4
4.83
Thorite
(Th)SiO
4
71.59
Uraninite (pitchblende)
UO
2
88.15
Uranophane
Ca(UO
2
)
2
Si
2
O
7
6H
2
O
40.59
is an alkali element and occurs mainly in alkali feldspars,
minerals, which may constitute ore horizons for mining
of potash.
Uranium and thorium have large ionic radii and are
comparativelyhighlycharged,sotheyrarelysubstitute
for other elements in common silicate minerals, but
Uranium can form either an oxide or a silicate and in
these forms may occur as a film along grain boundaries.
Quartz,feldsparandotherrock-formingmineralsmay
contain trace quantities of U and Th, but in the main
these occur in accessory minerals such as zircon,
monazite, sphene, rutile and xenotime. Uranium can
substitute for a variety of cations of similar size and
charge, for example thorium, zirconium, titanium and
calcium. The U-rich varieties of thorite (urano-thorite)
may contain more than 20% U. The degree of substitu-
tion of U and Th can vary widely, but the common rock-
forming minerals, such as feldspars, pyroxene etc, may
The relative abundance of these minerals means they
may represent a signi
cant component of a rock
'
sU
and Th content.
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