|
tems of lines Imost par
intersecting at allel to
C)0°. The Ion O. Often
gitudinal sec lint'rlam-
tionrectangu I ellated
lar with nu-
merous cleav
age lines par
allel to axisc^.
ing little from; appear
the perpen hexagonal
dicular to O. Cross sec-
Axial angle : tions ap-
usually very | parently
small —5°- jisotropous
1.3°, variable,! In con-
occasionally vergent
large, varying! polarized
with the |lightappa-
amount of
iron. Disp.
rently hex-l
agonal. I
As in
ene.
Rarely crys-
tallized in
rocks. Six
sided plates.
I
Perfect
II O, (in-
complete
Perfect
|0.
Never in crys-
tals, in rocks
usually as mi-
nute irregular
plates like
mica.
Scales and
hexagonal
plates I. O. as
though hex-
agonal. If
monoclinic I.
i-i^.O.
when
only rec-
ogniza
ble in po p
larized
light. _ _;
I Optical axis '
planes -L i-i^ Negative,
a almost -L O. Extinction
I Axial angle 'perpendic-
12-16° Disp.iular.
v<^9. ;
As me-
roxene.
Optical axis
plane -'- i-i'' a,
slightly varies
' from Q.\ a al-
most -L to O
j I^isp pyv.
I axial angle
usually large,
; 60-70°.
Optical axis
jplane || i-i^ \
to a line of
1 fracture, a
I almost at -^
toO.
Although oft-
; en seeming
hexagonal yet
i sometimes
obviously bi-
I axial with
I small axial
tangle a-i-O.
Negative,
stropg
Extinction
perpen-
dicular.
Apparent
ly rhomb
ic.
Negative,
feeble.
Extinction
apparent
ly rhomb-
ic.
Negative,
feeble.
Digitized by
Googk
TABLE XII.
Colors of
polarisa-
tion
Color and
index of re
fraction.
I Not par-
I ticularly
brilliant.
Browns.
In thin
I plates ir
Brown
black,
dark green
/3=i.6i.
Pleochro-
ism strong
; ridescent,' in long't.
I carmine sections a
red.
land b near
ly alike
In sections
parallel to
jc— axis
a-= yellow-
bright
I brown, at
' right an-
I gles<r
iC=brown-
black.
C>b>a.
Structure.
Primary, as
large crystals
(in eruptive
rocks) fre-
quently frag-
mentary or
Association
Usually
with
quartz and
ortho-
clase, also
with horn
with opaque blende,
I As merox-
'ene.
I Very bril
liant, irrid-
escent, red
to yellow.
Not very
brilliant,
blue-
green.
Red-br'wn
Pleochro-
ism feeb
ler than in
meroxene.
Colorless,
light green
oil green.
margin,
(comp. of
first order);
also in minute
scales particu-
larly in crys-
talline slates
or scattered
through the
magma, as in
basalts, etc.
(comp of sec-
ond order.
and more
rar'ly with
augite and
olivine.
Colorless,
white,
light
green.
Light to
dark green
«=i-.'>75-
Pleochro-
ism feeble
As primary in
large plates
In fasciculate
and radiate
aggregate. As
secondary in
aggregates of
minute irreg
ular .scales.
In crystalline
slates.
With oliv-
ine and
actinolite.
Inclusions. AUeralions
Generally
free from
inclusions,
but not
rarely
with fas
ciculale
masses of
epidote
needles or
regularly
arranged
slender
needles of
rutile.
Usually in ir
regularly felt
ed or rosette-
shaped radi-
ating aggre-
gates of mi-
nute scales.
Not in large
scales but like
talc as aggre
gates of mi-
nute irregular
scales radiate
or disperse.
With
quartz, or-
thoclase
tourma-
line.
-_
With
quartz, or-
thoclase,
mica or
with aug-
ite and
olivine.
With
quartz, or-
thoclase,
biotite.
muscovite
as primary
const.
Very poor
Rarely
needles of
rutile.
plates of
specular
iron, or
columns ol
tourma-
lin, or Zir-
con.
Into chlo
I rite like
I mineral,
I with epi
' dote and
calcite.
Loses its
brown col-
or, be-
comes
green, cal-
cite pene
f rates be
tween the
scales, nee
dies of ep-
idote ap-
pear. Also
formation
of limon-
ite or mag-
netite on
periphery.
Occurrence
In nearly
all rocks.
In many
as neces-
.sary pri
mary con-
stituent,
one ot the
first to ap
pear of the
minerals.
Product of
alteration
of augite,
horn-
blende,
rarely ol-
ivine.
Contact
mineral in
metamor
phic slates
Remarks.
Easily recog-
nized by the
cleavage and
strong pleo<
chroism. Cross
sections not
pleochroic as
hornblende
Not green as
chlorite, nor
fasciculate.
Very poor,
biotite, ac
tinolite.
As musco-
vite.
Poor,hem-
atite and
limonite,
needles of
actinolite
and rutile.
Becoming Rare in ol-
green to ivine store
colorless,
as above.
Occurrence.
Primary in granites
(in particular in tour
maline granites) and
crystalline slates,
gneiss, mica schists
and slate. In no other
rocks primary but as
product of alteration
in feldspars, chiasto-
lite. liebenerite. etc.
A primary conslit
ent in many crystal
line .slates. Not abun-
dant. Secondary pro-
duct of decomposition
of augites poor in iron
and hornblende, par-
ticularly Enstatite al
tered to olivine stone
and serpentine.
Difficult to
distinguish
microscopic-
ally from talc.
Sericite is but
an unctuous,
inelastic, light
green musco-
vite. which
occurs in ir-
regular scales
in certain
crystalline
slates.
Microchemi
cal treatment
of isolated
scales with
fluorosilicic
acid is the
surest test.
Primary in chlorite
slate. Decomposition
product of mica, au
gite. hornblende and
garnet.
Also hel-
minth, pen
nine, kaem-
mererite chlo-
ritoid, sismon-
dine, and ott
relite. Rare.
Digitized by
GoogI(
2. Crystals with
aa. Optical axis plane -J- i-i''; perfect
Name.
Chem.
Comp. and
Reactions.
Specif.
Grav.
Cleav-
age.
Usual combina-
tions and form
of sections.
Twins.
optical
determinants.
Double
refraction.
la. Or-
thoclase
K,(AySi,
2.50-2.59
Very
In grains or
Frequent.
Optical axis
Negative,
o«.
(2-57)
perfect
colnmnar,
(i)Oftenest
plane inclined
rather
Not
Be-
. i-i^ . I .
according
to forming an
strong.
attached
tween
2-i . 2-i^ . I .
to Karlsbad
an angle of t<f
In sections
by acids.
and
Sometimes tab-
type. Twin-
1 1^ with vertical
II i-i'' one
i-i^
ular or more
ning plane
axis.
direction of
angle
rarely, in min-
i-i.
c=b
extmction
8q°40^
ute crystals.
(2) Baveno
a : a = 5°
varies from
i i^ 1.0.
type. Twin
Real axial angle
the angle
2-i . I-i .
ning plant
2-i^
(^) Rarel)
Manebach
type.
=69°.
In sections || i-i^
or i-i a distorted
biaxial inter-
ferance figure
visible in con-
vergent pol.
light.
O.i-i
(=a . a)
by 5° 18^
Sections in
zone . i-i
extinguish
perpendic-
ularly.
lb.
Sani-
As
In slender rods
Twinning
If parallel i-i^
dtne.
above.
or large crystals.
plane=
b=b
Full of
almost never
0.
a : a=50°.
rifts.
granular. Sec-
tions II and i-i
elongate bands
truncate or
acute at the
ends. II i-i'' dis-
torted hexagons
with sides cor-
responding to
. I . i-i .
In the columnar
type, sections
rectangular if
perpendicular to
. i-i^ , if 2-i^
is present
octagonal.
Digitized by
GoogI(
MonoclinU Habitus.
cleavage |1 O and i-K; angle about 90®.
TABLE XIIL
Rather
brilliant,
but less
than as
quartz.
In thin
sections
often
less bril-
liant,
bluish
gray as in
nepheline
Colors of
Polariza
tion.
General-
ly cloudy
white or
gray.
rarely
clear.
Colored
red by
limonite,
Color.
Colorless
clear.
Structure,
In large crys-
tals or grains
of the first
order, more
rarely in small
grains or rods
in eruptive
rocks. Often
coalesced
with plagio'
clase. Zonary
structure is
rare as is
zonal arrange
ment of in-
clusions.
Association.
With
quartz,
biotite,
muscovite,
hornblende
and rarely
with augite.
plagioclase
and
elaeolite.
In eruptive
rocks as large
crystals of
first order ancj
minute rods
second order.
The large
crystals often
fractured.
Zonary
structure.
As
orthoclase
a so with
nepheline
and leucite
but never
with
muscovite
InclU'
sions.
In
general
poor.
Specular
iron,
biotiie
scales,
fluid
inclu-
sions,
needles
of
apatite,
zircon.
Very
rich.
Glass in
elusions,
usually
zonal in
arrange
ment.
augite
micro-
lites and
needles
of apatite
Altera-
tions,
Kaolini-
zation
with
forma-
tion,
of musco-
vite or
epidote.
One of the
most abun-
dant compo
nents in gran-
ular and por-
phyritic older
eruptives.
Essential
comp. in
granite, syen
ite. quartz
porphyry and
accessory in
nearly all
plagioclase
YOcV s. Also
in crystalline
slates as
gneiss, here
often glas-y
like sanidine
Almost
always
unaltered
Into opal
ande
sites and
trachytes
Occurrence,
Essential
eomp. (pri
mary) in
trachytes,
rhyolites,
phonolite,
and the glass
of orthoclase
rocks. In
nearly all
later plagio-
clase rocks.
Remarks,
Large crystals
may be recog-
nized by
twinning in
sections par-
allel to O and
-I and by the
oblique ex-
tinction paral-
lel i-i^ Mi-
nute rods of it
and sanidine
in the magma
of rocks often
greatly re-
semble neph
eline and cer
tain melilites,
Orthoclase
lacks, how-
ever, the iso
iropous hex-
agonal sec-
tions.
From plagio-
clase it may
be distin-
guished by
absence of the
polysynthetic
twins of the
latter.
Digitized by
GoogI(
bb. Optical
axial plane
II i-i^ ; perfect cleavage in 1=87°.
Name,
Chemical
comp. and
reactions.
specif.
Grav,
Cleavage,
Unsual combi-
nations b^ form
of sections.
Rarely in
Twins,
Optical deter-
minants.
Double re-
fraction.
I. Mono-
3 17-
Perfect
Very fre-
Optical axis
Positive,
clinic Au-
RSios
3-41
I
grains crys-
quent.
plane || i-i''.
^strong.
gite Group
R=Mg.
tals I. i-i. i-i^
twinning
acute bisectrix
Extinction
a. Common
Ca, Fe,
I and I-i. 0,
plane i-i,
=r in the ob-
in sections
and basalt
and Fe2
3.34-
>3^-
— 1 I=87°6^
also in pol-
tuse angle /?.
II b per-
ic augite.
O3 AI2 O3.
Sections per
ysinthetic
b=b^
p'^ndicu
According
pendicular to
twins.
The positive
lar; in sec-
to Tscher-
c octagonal
More rare-
axial angle
tions in-
^ mak a
with evident
ly inter-
enlarges with
clined to
mixture of
prismatic
penetrat
the amount of
i-i^ C: c
CaMgSi2
cleavage.
ing twins
iron in rhomb-
becomes
Og+Ca Fe
Longitudinal
in a plane
ic augite.
smaller
Si2 Og+
section dis-
of— I-i or
about 60°.
until it
xMg AI2 Si
torted hexag
1-2^
Sections || i-i
reaches
Og Scarce-
onal, with
and perpen-
when par-
ly attacked
cleavage lines
dicular to c
allel to i-i
by acids.
parallel to i-i''
quadrangular
often rhomb-
ic.
show the dis
appearance of
an optical
axis in almost
the middle of
the field.
In sections
II i-i^ c:
c=39° 54°
a:a=22°.
b. Dial-
do
3-23-
1(87°),
do-
do
do
lage.
3-34
shelly
fracture in
i-i.
c. Ompha-
do
3-3
As in au-
Only in
cite.
with more
AI2O3
gite, frac-
ture less
perfect
than in di-
allage.
grains.
rare
do
do
do
do
do
do
do
d. Diop-
more CaO
side.
than MgO
poor in
AI2O3
Also in long
columns with
transverse
do
do
do
Fracture
fracture.
in be-
usually not
e. Salite,
poor in
3-2-
sides the
terminated.
iron.
3-33-
above.
Section as in
augite.
Digitized by
GoogI(
TABLE XIV,
Color
and Re-
fraction
In section
green to
brown,
often vio-,
let brown
in basalt.
The same
I crystal
often ex-
hibiting
several
colots.
Pleochro-
ism usual-
ly feeble.
In phono-
lite it may
be strong.
Structure.
In large
I crystals
(I. O.)
with zonal
Association
Chiefly
with pla-
gioclase,
Inclusions.
Decompositioft .
alternating nepheline.
colors. In- leucite,
twins with or
these ' without
bands pass olivine
through ( and bio-
both. Oft- tite. Rare-
en with so-
called
**hour-
glass"
form. when
Greenish
brown.
Pleochro-
ism very
feeble.
Grass
green.
do
Light
green-
colorless.
Relief
strong.
ly with
ortho-
clase,horn-
blende,
and
I
sections quartz.
parallel to I
i-i fall into,
4 areas.
Also in I
columns j
and micro-
Utes(lI.O.)'
crystals
often in
large ag-
gregates &
radial
Abundant Into chlorite,
glass inclu- calcite, limon-
isions, apa | ite. epidote
! tiie nee- ' and quartz,
f dies and ps'udomorphs
! magnetite, of any of these
! ! after augite.
Into opal.
More rarely
into horn-
blende, the
form being re-
tained but the
cleavage that
ofhorpblende.
Into serpen -
tine with talc
and chlorite.
groups.
Only as
large ir-
regular
grains. In
inclusions,
in fibrous
and twin
ning char-
acters
much as
bronzite.
Often co-
alesced
with ordi-
nary >ug-
ite, horn-
blende or
Only in un
altered
gr'ins poor
in inclu-
sions. Oft-
en coalesc-
ed with
horn-
blende.
With pla-
gioclase,
common
augite, ol-
ivine,
horn-
blende,
and rarely
with
quartz.
(c) With
quartz,
horn-
blende,
garnet, zo-
isite, dis-
thene, and
ruiile.
(d) With
olivine,
chromite,
diallage, &
rhombic
augite.
(e) quartz,
horn-
blende,
scapolite,
plagio-
clase, and
titanite.
Like
bronzite
with inclu-
sions of
brown
scales of
goethite?
parallel to
i-i. other
wise poor
in inclu
(c) Rare,
fluid and
rutile nee
dies.
(d) Rarely
glass in
elusions.
At the ends
changes into
dark green
strongly pie
ochroic horn-
blende fibres.
Into viridite,
also serpen-
tine with for-
mation of
chlorite and
talc.
Occurrence.
Remarks.
Later porphy- 1 Easily recog
ritic eruptives
as essential
and primary,
in diabase, I,
augite ande-
site, and all
basalts, also
andesites, tra-
chytes, phon-
olites. Rarely
in large grains
in older erupt-
ives and crys-
talline slates.
nized by ob-
liquity of ex-
tinction of c."
c. the prismat
ic cleavage
with angle of
87°, especially
in cross sec-
tion. Liable
to be confused
with horn
blende in sec-
tions inclined
to c. When
augite is near-
ly "colorless its
polarization
colors are;
vivid and like
olivine.
Primary abun-
dant ill gab
bro, norite,
rare porphy r
itic eruptives
In olivine
stone and ser
pentine. Rare
in crystalline
slates.
(c) In eclcg
ite and am-
phibolite
(d) In olivine
stone (prima-
ry) rarely sec
ondary altera-
tion of garnet
(e) In crystal
line slates.
Often similar
to bronzite
in sections or
plates parallel
to i-i easily
recognized.
Colors lighter
than in augite I
proper (less
iron). Differ
from diallage
in absence of
complete
fracture in
Digitized by
GoogI(
Name,
Chem.
Comp. and
reactions.
Specif.
Grav.
Cleavage.
Usual, com-
binations df
form of Sees.
In grains or
Twins
Opticial
determinants
-
Double
Refract.
Colors of
Polariza-
tion.
f. Acmite.
Na2 (Fe-i)
3-53-
Complete
i-i
As augite.
As
As
Si, O,,
3.55
187°,
incom-
plete
i-i.
long flat-
tened col-
umns
(planes i-i
being
largest.)
I . i-i . i-i^
fre-
quent.
augite.
augite.
Pleochro-
ism rath-
er strong.
C=dark
brown.
a=
brownish
g. Wallas-
Ca Si O3
2.78-
Parallel
1=87°
do
Opt. axis
Positive,
green.
tonite.
Completely
decompos'd
2.91
i-i,
and I-i
Almost
always in
plane
II i-i^-
strong, c
forms an
c>b>a^
separating
irregular
Apparent
angle with
Very
galatinous
fibrous
axial
Oof32°-l2^
brilliant.
silica.
long prisms
angle -=70°
a:c=i2°
cc.
Complete
2. Horn
mRSiO.^ +
3.1-
I very
I . i-i^ . i-i
Fre-
Opt. axis
Negative,
Less
blende
n(R2)b3.
3-3
perfect
and . I or
quent
plane || i-i^.
rather less
brilliant
Group.
R=Ca, Mg
with
i-i^ almost
i-i
Acute bisec-
strong than
than in
Common^
Fe.
angle of
always in
trix=a
augite.
augite,
Basaltic
R2 = (AI2)
124° 11^;
crystals.
falls in the
Extinction :
yellow,
Hornblende
(Fe2 ).
i-i and
Cross sec-
obtuse
C:c= about
green,
[b. Smar-
When
i-i^
tions usual-
angle /3,
if (2-18°)
brown.
agdite
containing
imperfect
ly hexagons
6=b. Real
a : c=75«
Compare
much iron,
also octago-
axial angle
a : a^=29°
uralite.Oc-
attacked
nal, longit.
about 79°.
38^
curs with
slightly by
sections as
Positive
C:c=i3-
omphacite
acids.
augite.
axial angle
.^5°
garnet,
varying
in green,
zoisite. and
with amt
1 1-13° in
rutile.]
of Fe. Opt.
axis disap
brown
hornblende
Ca Mg3 Si,
3.026-
As
Long
More
pears on
c. Actino-
0,2+CaFe3
3.16
above.
columns
rarely.
edge of
lite.
Si,0,,
(Techer-
mak)
No Al.
fracture
trans-
verse.
usually not
terminated
I . i-i^
field
II and i-i.
((
little iron.
3MgSi03+
I
I. i-i
[C:clS°]
d. Tremo-
CaSiOa
2.93-3
as above.
long
lite.
Preponder-
ating
slender
columns.
((
((
Very
brilliant.
*
MgO.
(See next
Insoluble.
table.)
Digitized by
GoogI(
TABLE XV.
Color etc.
Dark
brown-
dark
green
/3=over
1.7.
Colorless
yellowish
white.
strong
relief.
Structure.
In large crys-
tals in syenite,
often frayed
at the end. In
minute crys-
tals yellow or
dark green in
trachytes and
phonolites.
In fasciculate
or radiate
aggregates,
Association
Withelae-
olite. soda-
lite, micro-
line, and
biotite
With cal-
cite, green
augite,
granite.
Inclu-
sions.
Alterations.
Metallic
particles.
Fluid in-
clusions.
Occurrence.
Remarks,
Not rare in elaeolite-syenite,
Phonolite, and trachytes.
(g) as product
alteration of
contact miner-
al rare in
granular
limestones,
which have
been the re-
sult of meta-
merphism.
Rarely in
phonolite etc.
(g) Very similar to
tremolite, distin-
guished by angles
of the prisin ind
solubility .
Difficult to distin-
guish from zeolitic
substances as
scolezite.
cleavage 1= 1 24°
Green-
brown.
/3p=i.62
|Pleochro-
ism rath-
er strong
a= yel-
lowish
green or
honey
yellow.
b=yel-
lowish
brown.
C=black
or green
ishbrown
c>b>a.
Light to
dark
green.
pleochro -
ism
feebler
C=dark
green.
a=yel-
lowish.
Colorless
In large crys
tals or grains
O . rarely
in small crys
tals and mi-
croliths II. O .
Green horn
blende often
fibrous, brown
zonal. Green
bomb, often
coalesces with
augite.
Needles or
grains often
fibrous.
In columns
and fasiculate
aggregates.
With
Poor.
orthoclase
Fluid in-
plagio-
clase,
clusions,
glass and
quartz, bi-
otite rare-
gas pores.
Metallic
ly with
augite and
olivine.
particles
and
apatite
needles.
With
Very
quartz.
poor.
mica,
chlorite
and rutile.
With cal.
cite, oli-
vine, horn-
«<
blende,
and
diallage.
Yellowish
fibrous, epi-
dote, calcite
and limonite,
Often on the
surface to
magnetite ;
augite. Into
biotite, chlo
rite.
Occurrence.
(c) Rather
frequent in
certain crys
talline slates
lacking feld-
spar as talc-
mica-and
chlorite-
schists and in
serpentine,
(d) As con
tact mineral in
hmestone. As
primary (rare-
ly secondary)
component in
slates and
serpentine.
Primary
essential in
granular and
porphritic
eruplives, as
syenite,diorite
(green) por-
phyrite, ande-
site, trachyte
(brown).
Accessory in
besalt (brown)
olivine stone
(green) rare.
In crystalline
slates (green)
abundant.
Essential in
amphibolite
slates and
certain gneiss.
Distinguished
from augite by
prismatic cleavage
angle, slight in
clination of C : c
and strong pleo-
chroism. Biotite
has not the cleav
age and dichroism
in sections parallel
O.
(c) Almost al-
ways in long col
umns not in short
crystals as in ordi-
nary hornblende.
(d) compare
woUastonite.
Digitized by
GoogI(
(e.) ArfvedsonUe. Na, (Fej'i Si^ O12. Specif, gr. 3.33-3.59- Occurs in large
grains cleaving in I, with orthoclase, microcline. elaeolite and sodalite, rarely in elaeolite
rocks. It is distinguished from hornblende by blue»grcen color and composition .
(b.) Glatuophane. Na2 ( AI2 ) Si4 O12 with Ca Mg. and Fe. Specif, gr. 3.1.
It is an indigo blue mineral with strong pleochroism occurring in long fibrous needles
dd. Cleavage || O and i-i; angle 115°.
Name.
Chemical
comp. and
reactions.
Specific
^avity
Cleavage.
Usual combi-
nations and
form of sec s.
Twins.
Optical deter-
minants.
Double re
fraction.
Epidote,
H2 Ca4
3-32-
|0 perfect
Extended in
Plane i-i
Optical axis
Negative,
( R2 )3 Sie
35
and i-i
the ortho-di-
Rarely
plane || i-i^
strong.
O26.
forming
agonal, gen-
micro-
b=b acute
Extinction
angle of
erally small
scopic.
bisectrix =a
a: c=2°
115° 24^
columns I. 0.
I-i. i-i. Lon-
gitudinal sec-
tions II i-i^
hexagonal.
Cross sections
II O: i-i elong
ate quadrang-
ular or ex-
tended hex-
agonal. Also
in grains.
nearly coin-
cides with c.
Sections |j to
i-i show a bi-
axial interfer-
ence figure.
20\
c: a^=27°
47^=c:0.
ee. Cleavage imperfect in I or|
Titanite.
Ca Si Ti
3- 4 -3-6
i-i^ii3°
Usually crys-
Rather
Optical axis
Positive;
O5. De-
talline I. 0.
frequent
plane || i-i'' strong. |
composed
3c/, im-
j^(i-i^) V2
Contact
acute bisectrix
Extinction
by H2 SO^
perfect.
(1-2^) or %
or mter
=<:almost per-
a: c=39°
i7^a-a'^=
Ti O2 is
(1-2O. Or in
pene-
pendicular to
dissolved,
wedge-shaped
trating
^(i-i) strong
21°.
and gyp-
grams.
twins in
dispersion of
sum
*
plane O.
axes.
formed.
Gypsum.
Ca S0,-|-
2.2-2.4
Complete
In grains or
Rare in
Optical axis
Negative
2 Aq. Sol-
in the cli-
long colamnar
micro-
plane || i-i^
strong.
uble in
nodiago-
individuals.
scopic
Acute bisect.
Extinc-
acids with
nal, less so
Crystals I.
individ-
=^z. One op-
tion
difficulty.
-I.
i-i^ -I.
uals.
tical axis al-
most -L i-i
forming with
c an angle of
87,°, the other
an angle of
22^
a: c=52°
3</
c: c=37°
3C/.
Digitized by
GoogI(
often coalesced with hornblende, rarely in crystalline slates, eclogite, amphibolite, mica
and chlorite.slates.
(g.) Uralite (Smaragdite in part) has the composition of hornblende but has a
cleavage similar to augite. It is a proluct of the decomposition of augite and diallage.
It occurs in gabbros and serpentine as well as augite porphyry.
TABLE XVL
Colors of
polariza-
tion.
Color and
index of re
fraction.
Structure.
Association
Inclu-
sions.
AUera-
tions
Occurrence
1 -
Remarks.
Citron yel-
— '\ • -
'
Very bril-j low, yel-
In long mi-
With
Very
Secondary
Similar to au-
lliant, yel- lowish
nute columns
quartz, or-
poor.
frequently
gite. Charac-
low tored.jgreen.
13=1.72-
1.75. Pie-
in chloritic
thoclase,
Fluid
,as decom
teristic is the
substance or
plagio -
inclu-
! position
|