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Three new miner
als in
the dumor
tieri
te su
pergrou
p were discovered in
the Szkl
ary
pegm
ati
te, Lower Silesi
a, Pol
and. Niobohol
ti
te, endmember (Nb
0.6□
0.4)Al
6B
3Si
3O
18,
and
ti
tanohol
ti
te, endmember (Ti
0.75□
0.25)Al
6B
3Si
3O
18,
are new members of
the hol
ti
te grou
p, where
as szkl
aryi
te, endmember □Al
6B
pan class="inline-formula" id="inline-formula-2">ass="math mml" alt="Formula" src="2841/embed/mml-math-2.gif" /> pan>O
15, is
the firs
t re
presen
tative of
a po
ten
ti
al new grou
p. Niobohol
ti
te occurs mos
tly
as overgrow
ths no
t exceeding 10 μm in
thickness on cores of hol
ti
te. Ti
tanohol
ti
te forms
patches u
p to 10 μm
across in
the hol
ti
te cores
and s
tre
aks u
p to 5 μm wide
along bound
aries be
tween hol
ti
te cores
and
the niobohol
ti
te rims. Szkl
aryi
te is found
as
a patch ~2 μm in size in As-
and Sb-be
aring dumor
tieri
te enclosed in qu
ar
tz. Ti
tanohol
ti
te crys
tallized
almos
t simul
taneously wi
th hol
ti
te
and o
ther T
a-domin
an
t miner
als such
as
tan
tali
te-(Mn)
and s
tibio
tan
tali
te
and before niobohol
ti
te, which crys
tallized simul
taneously wi
th s
tibiocolumbi
te during decre
asing T
a ac
tivi
ty in
the
pegm
ati
te mel
t. Szkl
aryi
te crys
tallized
af
ter niobohol
ti
te during
the fin
al s
tage of
the Szkl
ary
pegm
ati
te form
ation. O
ptic
al
pro
per
ties could be ob
tained only from niobohol
ti
te, which is cre
amy-whi
te
to brownish yellow or grey-yellow in h
and s
pecimen,
tr
anslucen
t, wi
th
a whi
te s
tre
ak, bi
axi
al (–), n
α = 1.740 – 1.747, n
β ~ 1.76, n
γ ~ 1.76,
and Δ &l
t; 0.020. Elec
tron micro
probe
an
alyses of niobohol
ti
te,
ti
tanohol
ti
te
and szkl
aryi
te give, res
pec
tively, in w
t.%: P
2O
5 0.26, 0.01, 0.68; Nb
2O
5 5.21, 0.67, 0.17; T
a2O
5 0.66, 1.18, 0.00; SiO
2 18.68, 21.92, 12.78; TiO
2 0.11, 4.00, 0.30; B
2O
3 4.91, 4.64, 5.44; Al
2O
3 49.74, 50.02, 50.74; As
2O
3 5.92, 2.26, 16.02; Sb
2O
3 10.81, 11.48, 10.31; FeO 0.51, 0.13, 0.19; H
2O (c
alc.) 0.05, –, –, Sum 96.86, 96.34, 97.07, corres
ponding on
the b
asis of O = 18–As–Sb
to {(Nb
0.26T
a0.02□
0.18)(Al
0.27Fe
0.05Ti
0.01)□
0.21}
Σ1.00Al
6B
0.92{Si
2.03P
0.02(Sb
0.48As
0.39Al
0.07}
Σ3.00(O
17.09OH
0.04□
0.87)
Σ18.00, {(Ti
0.32Nb
0.03T
a0.03□
0.10)(Al
0.35Ti
0.01Fe
0.01)□
0.15}
Σ1.00Al
6B
0.86{Si
2.36(Sb
0.51As
0.14)}
Σ3.01 (O
17.35□
0.65)
Σ18.00 and {□
0.53(Al
0.41Ti
0.02Fe
0.02)(Nb
0.01□
0.01)}
Σ1.00Al
6B
1.01{(As
1.07Sb
0.47Al
0.03) Si
1.37P
0.06}
Σ3.00(O
16.46□
1.54)
Σ18.00. Elec
tron b
acksc
attered diffr
ac
tion indic
ates
th
at the
three miner
als
are
presum
ably isos
truc
tur
al wi
th dumor
tieri
te,
th
at is, or
thorhombic symme
try, s
pace grou
p Pnma (no. 62),
and uni
t-cell
par
ame
ters close
to
a = 4.7001,
b = 11.828,
c = 20.243 Å, wi
th
V = 1125.36 Å
p>3p>
and
Z = 4; micro-R
am
an s
pec
trosco
py
provided fur
ther confirm
ation of
the s
truc
tur
al rel
ationshi
p for niobohol
ti
te
and
ti
tanohol
ti
te. The c
alcul
ated densi
ty is 3.72 g/cm
p>3p> for niobohol
ti
te, 3.66 g/cm
p>3p> for
ti
tanohol
ti
te
and 3.71 g/cm
p>3p> for szkl
aryi
te. The s
tronges
t lines in X-r
ay
powder diffr
ac
tion
patterns c
alcul
ated from
the cell
par
ame
ters of dumor
tieri
te of Moore
and Ar
aki (
pan id="xref-ref-14-1" class="xref-bibr">1978pan>)
and
the em
piric
al formul
ae of niobohol
ti
te,
ti
tanohol
ti
te
and szkl
aryi
te
are [
d, Å,
I (
hkl)]: 10.2125, 67, 46, 19 (011); 5.9140, 40, 47, 57 (020); 5.8610, 66, 78, 100 (013); 3.4582, 63, 63, 60 (122); 3.4439, 36, 36, 34 (104); 3.2305, 100, 100, 95 (123); 3.0675, 53, 53, 50 (105); 2.9305, 65, 59, 51 (026); 2.8945, 64, 65, 59 (132), res
pec
tively. The
three miner
als h
ave been
approved by
the IMA CNMNC (IMA 2012-068, 069, 070)
and were n
amed for
their rel
ationshi
p to hol
ti
te
and occurrence in
the Szkl
ary
pegm
ati
te, res
pec
tively.
p>