Diopside from the Atwater Quarry area, Westfield, Massachusetts


Shelton, W.; Robinson, G.W.; Burgess, D.; Levine, D.

Rocks and Minerals 79(5): 344

2004


ous
monoclinic
symmetry
(unlike
some
datolite
that
mim-
ics
orthorhombic
symmetry).
As
a
consequence,
the
twin-
ning
is
clearly
shown
by
reentrant
angles
formed
by
equiva-
lent
faces
of
the
two
crystals
where
they
meet.
This
specimen
was
reported
to
one
of
us
(MLW)
as
one
of
four
or
five
sim-
ilar
twinned
crystals
that
were
found
together.
The
occurrence
of
twinning
in
datolite
is
clearly
estab-
lished
by
these
specimens,
together
with
the
one
described
by
Whitlock.
In
both
cases,
the
twin
law
appears
to
be
the
same,
though
definitive
morphological
studies
of
the
cur-
rent
material
are
not
yet
complete.
Relative
to
a
unit
cell
with
a
=
9.636A,
b
=
7.608A,
c
=
4.832A,
and
beta
=
90.40°,
the
twin
law
is
penetration
by
reflection
across
{100}.
The
penetration
nature
of
the
twin
is
not
obvious
but
is
indicat-
ed
by
the
irregular
surface
shown
schematically
by
a
dashed
line
in
two
of
the
drawings.
Comparison
of
the
twinned
and
untwinned
crystal
will
demonstrate
that
the
faces
that
form
a
prismatic
zone
parallel
to
the
c-axis
must
belong
partly
to
one
individual
of
the
twin
and
partly
to
the
other.
Although
twinning
can
certainly
be
said
to
be
rare
in
datolite,
it
is
worth
noting
that
datolite
is
isostructural
with
herderite,
and
twinning
is
very
common
in
herderite.
It
is
unclear
why
twinning
is
common
in
one
species
and
rare
in
another
with
a
similar
structure.
MINERALOGY
OF
THE
HIDDENITE
AND
EMERALD
VEIN
ASSEMBLAGE,
HIDDENITE,
NORTH
CAROLI-
NA.
M.
A.
Wise
1
,
A.
J.
Anderson
2
,
and
R.
L.
Isaac
s
:
1
Dept.
of
Mineral
Sciences,
Smithsonian
Institution,
Washing-
ton,
DC
20560;
2
Dept.
of
Geology,
St.
Francis
Xavier
University,
Antigonish,
NS,
Canada
B2G
2W5.
Emerald
and
hiddenite
occur
in
cavities
found
in
steeply
dip-
ping
quartz
veins
that
cut
migmatitic
host
rocks
at
the
Rist
property,
Hiddenite,
North
Carolina.
The
quartz
veins
are
typically
1-10
cm
wide
and
crosscut
all
lithologies,
with
no
apparent
relationship
between
the
mineralogy
of
the
host
rock
and
the
presence
or
absence
of
emerald
or
hiddenite.
Many
of
the
quartz
veins
developed
cavities
that
contain
a
suite
of
minerals
including
albite,
apatite,
beryl,
calcite,
chabazite,
clinochlore,
goethite,
graphite,
kaolinite,
mus-
covite,
molybdenite,
pyrite,
pyrrhotite,
quartz,
rutile,
siderite,
spodumene,
and
tourmaline.
Examination
of
six
veins
revealed
four
basic
assemblages
characterized
by
a
specific
group
of
minerals:
a
calcite
assemblage,
an
amethyst
assem-
blage,
a
hiddenite
assemblage,
and
an
emerald
assemblage.
In
general,
quartz
and
calcite
are
found
in
multiple
gener-
ations:
Quartz
occurs
as
early-crystallized,
fine-grained,
doubly
terminated
crystals;
large
clear
or
milky
crystals;
and
late
amethystine
scepters.
Calcite
crystals,
many
of
which
are
fluorescent,
show
hexagonal
prisms,
scalenohedra,
and
platy
and
rhombohedral
forms.
Hiddenite,
emerald,
muscovite,
and
albite
generally
appear
to
have
formed
slightly
later
than
quartz
or
calcite.
Pale
green
to
emerald-green
hiddenite
is
typically
etched
and
coated
by
thin
films
of
black
to
green
344
ROCKS
&
MINERALS
clinochlore.
Emerald
is
often
associated
with
quartz,
albite,
and
goethite
pseudomorphs
after
siderite.
Muscovite
forms
tan-colored
crystals,
sometimes
with
greenish
rims.
Rutile
tends
to
form
thin
elongated
silver
to
black
crystals
scattered
on
the
matrix
of
fine-grained
quartz
or
calcite.
However,
when
found
in
the
emerald-bearing
veins,
rutile
often
forms
reticulated
twins.
Crystallization
of
sulfides,
chabazite,
and
clays
generally
took
place
near
the
final
stages
of
cavity
devel-
opment.
Almost
all
of
the
cavities
examined
contained
minute
pyrite
cuboctahedra
scattered
on
quartz,
calcite,
and
muscovite.
Microscopic
crystals
of
water-clear
twinned
chabazite
are
uncommon
in
most
cavities
but,
when
present,
are
often
perched
on
muscovite,
calcite,
and
quartz.
DIOPSIDE
FROM
THE
ATWATER
QUARRY
AREA,
WESTFIELD,
MASSACHUSETTS.
W
Shelton
1
,
G.
W
Robinson,
D.
Burgess,
and
D.
Levine:
1
19
Highland
Ave.,
Westfield,
MA
01085;
2
A.
E.
Seaman
Mineral
Museum,
Michigan
Technological
University,
Houghton,
MI
49931-
1295.
Recent
finds
of
diopside
in
the
vicinity
of
the
Atwater
quar-
ry
near
Westfield
include
some
of
the
largest
crystals/cleav-
ages
known
from
Massachusetts
and
possibly
anywhere
else.
The
host
rock
appears
to
be
nearly
solid
diopside
with
minor
actinolite.
Adjacent
rock
layers
are
dolomitic
marble
bands
that
carry
actinolite
needles.
This
small
deposit
is
sig-
nificantly
different
from,
and
probably
unrelated
to,
nearby
ultramafic
talc-serpentine
occurrences
that
trend
north-
south
across
the
eastern
edge
of
the
Berkshire
Mountains.
Diopside
cleavages
to
65
cm
have
been
recovered
along
with
significant
amounts
of
actinolite.
Larger
cleavages
may
be
observed
in
the
rock,
but
recovery
is
problematic.
Well-
formed
individual
crystals
exhibiting
typical
pyroxene
mor-
phology
have
also
been
found
but
are
generally
much
small-
er
and
more
restricted
in
occurrence.
Calcite,
quartz,
epidote,
magnetite,
chlorite,
and
rare
uvite-dravite
are
also
present
in
lesser
quantities.
Quantitative
energy
dispersive
X-ray
spectrometry
analyses
indicate
typical
composition
for
the
diopside
and
composition
for
the
epidote
that
is
somewhat
enriched
in
Mg,
though
surface
contamination
by
dolomite
cannot
be
ruled
out
because
of
the
sampling
procedure
used.
This
may
warrant
further
investigation,
as
presently
there
are
no
known
REE-free
members
of
the
epi-
dote
group
that
are
Mg-dominant,
though
Ford
(1968)
does
note
a
magnesian
variety,
"picroepidote."
One
question
remains
unanswered—how
did
the
diop-
side
in
this
particular
deposit
survive
while
other
occur-
rences
in
the
immediate
area
are
nearly
completely
altered
to
actinolite
or
talc?
At
the
nearby
Atwater
quarry,
once
a
source
of
soapstone
and
serpentine
marble,
there
are
dis-
tinct
pseudomorphs
of
talc
replacing
diopside
that
preserve
the
parting
planes
characteristic
of
the
species.
A
similar
pattern
of
replacement
and
alteration
is
repeated
at
several
localities
along
the
talc-serpentine
belt
in
Massachusetts.
An
Introduction
to
Crystalline
Quartz
uaitz
This
book
on
Quartz
is
njoyable,
educational
114tternationally
lined.
The
internal
ructure
and
external
forms
are
simply
yet
technically
explained.
Illustrated
with
beautiful
photos
and
available
in
soft
cover
and
hard
cover
with
interactive
CD
ROM.
For
detailed
information
www.quartzbook.com
©2003
Dibble
Trust
Fund
Ltd.
cL
SUPERB
PRINTING
AWARD
GOLD
AWARD
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Despite
its
proximity,
the
diopside
locality
appears
to
be
sig-
nificantly
different
from
these
deposits
and
either
spatially
or
temporally
isolated
from
the
retrograde
alteration
event
that
produced
them.
REFERENCE
Ford,
W.
E.
1968.
Dana's
textbook
of
mineralogy.
4th
ed.
New
York:
John
Wiley
&
Sons.
REDUCED
SILICON,
IRON,
AND
OTHER
UNUSUAL
SPECIES
IDENTIFIED
IN
A
FULGURITE
FROM
FARM-
INGTON,
CONNECTICUT.
A.
A.
Sheffer
t
and
B.
M.
Jarnot
2
:
1
Lunar
and
Planetary
Laboratory,
University
of
Arizona,
Tucson,
AZ
85721;
2
12
Davis
Rd.,
Tyngsboro,
MA
01879.
Petrographic
studies
have
begun
on
a
fulgurite
that
formed
in
August
2002
near
the
intersection
of
Routes
6
and
177
in
Farmington,
Connecticut.
This
occurrence
resulted
from
the
combined
energies
of
a
lightning
strike
and
a
downed
high-
voltage
(27
kV)
aluminum
power
line,
which
struck
the
edge
of
a
paved
road
(Route
177)
and
traveled
laterally
into
the
berm
and
parallel
to
the
roadway.
The
downed
power
line
remained
energized
for
several
hours
and
heated
an
area
sev-
eral
feet
away
from
the
initial
lightning
strike;
however,
a
con-
tinuous
melted
area
connected
the
apparent
impacts
of
both
power
sources.
Melted
source
material
consisted
primarily
of
sand
and
crushed
basalt
gravel,
with
asphalt
macadam
pro-
viding
abundant
hydrocarbons
near
the
surface
to
produce
a
heterogeneous
carboreductive
furnace
environment.
Alu-
minum
from
the
power
line
appears
to
have
also
contributed
to
the
melt
composition
and
reduction
in
certain
areas.
The
entire
fulgurite
branches
6
meters
laterally
to
a
maxi-
mum
depth
of
0.5
meter
and
contains
at
least
five
distinct
zones,
characterized
by
different
degrees
of
heating
and
chemical
reduction.
Under
the
power
line
and
nearest
to
the
surface
is
an
area
of
dark
green
glass
with
large
vesicles.
Fur-
ther
beneath
the
surface
and
connecting
the
strike
zones
is
an
area
of
degassed
dark
green
glass
with
centimeter-sized
Fe
metal
inclusions.
Directly
at
the
surface
of
the
lightning
strike
is
a
small
area
of
gray
glass
containing
Fe-Si-Al-Ti
metallic
droplets.
Below
the
surface
and
extending
laterally
away
from
the
strike
is
frothy,
pale
green
glass
with
smaller
metallic
droplets.
Farthest
away
from
the
strike
and
the
power
line
is
an
area
of
tubular,
linear
fulgurite
structure.
Partially
melted
rocks
and
sand
cemented
by
glass
coat
the
outside
of
all
samples.
Microprobe
studies
have
begun
using
a
Cameca
SX50
elec-
tron
microprobe
with
a
voltage
of
15
kV
and
a
current
of
20
nA
to
obtain
backscattered
electron
images
and
point
analy-
ses.
Preliminary
analyses
indicate
a
large
array
of
reduced
metals,
including
metallic
Si,
Fe,
Fe
2
Si,
FeTi(A1,Si)
2
,
Fe(A1,Si)
3
,
Fe(A1,Si)
5
,
and
Fe
5
A1Si
lo
.
Many
metallic
species
appear
to
be
iron
silicides
similar
to
those
found
previously
in
fulgurites,
but
here
aluminum
is
replacing
the
silicon.
In
addition
to
the
unusual
metals,
this
fulgurite
contains
large
amounts
of
heterogeneous
silicate
glass
with
relict
SiO
2
crys-
tals,
lechatelierite,
mullite,
and
A1
2
0
3
,
which
appears
to
be
growing
from
the
melt.
Volume
79,
September/October
2004
345