CHEMICAL PETROLOGY AND MINERALOGY OFHORNBLENDES IN N

GRANIRTHWEST ADIRONDACKIC ROCKS*

A. F. BullrNGroN, Princelon (/ niversi,ty, Princeton, N ew Jersey

AND

B. F. LnoNann, gical Surt:ey, Dentter, Colorado

TS

Abstract .Introduction. .Petrologic Notes.

flornblende from granitic rocks ofHornblende from younger granitic

Stark complex.

Oot ical and Chemical Dala. . .Optical properties of some Adi hornblendes.

Indices oI re l ract ion. .

Birefringence ..

Optic axial angleDispersion. .Extinction angle.Pleochroism and absorption.

General relations of the Adirondack

Relerences.

891891892892893897897897898898899899900900901

belong to the femaghasl ingsi te and ingsite varieties and carry chlorine as well as

fluorine in significant amounts. The varia ions in composition of the hornblendes correlate

with the deEree of difierentiation of the of which thev are a part, or with the degree of

l. The methods used in determining the optical

discussed. A satisfactory, detailed correlationmodification of incorpotated foreignproperties are fully described and criticaof chemical and optical properties has yet been achieved, even for the limited part of

the hastingsite group investigated herg.

INr

Chemical analyses and optical prope

the northwest Adirondack Mountains,have been recalculated in terms of a t

Granitic rocks with hornbmasses and are a major elemen

northwest Adirondack X,Iountain

blendes. .

of seven hornblendes from granitic rocks of

York, are presented. The chemical analyses

ical amphibole formula. All the hornblendes

ODUCTION

as a varietal mineral form very large

in the pre-Cambrian bedrock of the

of New York (Buddington, 1939 and

ion on the chemical composition and

ndes, together with a brief discussionBuddington initiated the study of the

1948). This paperoptical propertiesof their petrologic

is a contribuof the hornblenvironment.

U. S. Geologicai Survey.x Publication authorized by the

891

892 A. F. BUDDINGTON AND B. F. LEONARD

hornblendes and prepared the section on chemical petrology. Leonardcontributed the optical data.

The chemical analyses were made at the Rock Analysis Laboratory ofthe University of l,Iinnesota. The cost of the analyses was borne by agrant of funds from the Eugene Higgins Trust allocated to PrincetonUniversity.

The hornblendes were concentrated for analysis by use of the Frantzmagnetic separator and heavy liquids. This work was done by H. L.James and R. J. Smith. The hornblende concentrates submitted forchemical analysis were better than 99.5 per cent pure. lVlost of themwere about 99.9 per cent pure. The contaminants were chiefly minutegrains of qtartz and potash feldspar that had not broken free from thehornblende, even after crushing to -100, *200 mesh.

There is no reason to doubt that the hornblendes in the fractionstudied optically were identical with those in the concentrate submittedfor chemical analysis.

The writers have followed Bil l ings' subdivision (1928) of the hastings-ite group, according to the molecular proportions of FeO and MgO;Jerrohasti.ngsite, FeO/MgO)2; femaghastingsite, FeO/MgO 12 bfi )!;and magnesiohastingsite, FeO/MgO < j.

PBtnorocrc NorBs

The granitic rocks of the northwest Adirondacks are of two difierentages. The older granitic rocks, part of the Diana-Stark complex, havebeen intensely deformed, recrystallized, and intruded by a younger seriesof granitic rocks. These younger granites in large part have a sheetlike,phacolithic, and domical relationship to all older rocks.

Chemical analyses of rocks from which the hornblendes 1, 3, 4, and 6(Table 1) and pyroxene no. 8 (Table 1) were concentrated are to appearin a forthcoming publication of the U. S. Geological Survey entit led"Geology and mineral deposits of the St. Lawrence County magnetitedistrict, New York," by Buddington and Leonard.

Hornblende Jrom Granitic Rocks of Diana-.Stork Complex

The older granitic rocks are facies of the Diana-Stark complex. Thiscomplex has been described and interpreted (Buddington, 1939, pp. 73-109; Buddington, 1948, pp.2a-29) as a very great sheet of igneous rockthat has been intensely deformed and recrystall ized. The sheet has astratiform character resulting from difierentiation primarily by frac-tional crystallization. Pyroxene syenite gneiss with lenses of shonkiniteand feldspathic ultramafic (ferroaugite, ilmenite, and magnetite) gneissoccurs in the lower part. This grades upward through pyroxene qlf,artz

HORNBLENDE IN NORTHWES:I ADIRONDACK GRANITIC ROCKS 893

syenite gneiss and hornblendic quartz-bearing syenite gneiss into horn-

blende granite gneiss, which forms the upper facies. The pyroxenic facies

of this sheet are green in color, whereas the hornblendic facies are pink.

Hornblende 5 occurs as porphyroblasts in a pink granoblastic quartz-

bearing syenite gneiss, which grades into a pyroxene quartz-bearing

syenite gneiss stratigraphically below and a hornblende granite gneiss

stratigraphically above. Hornblendes 6 and 7 are from wholly recrystal-

lized granite gneiss characteristic of the upper facies of the Diana-Stark

sheet. The variation of the mafic minerals from ferroaugite (nos. 8 and 9,

Table 1) in the lower part of the sheet through femaghastingsite (no. 5)

to ferrohastingsite (nos. 6 and 7) in the upper part of the sheet is con-

sistent with what might be expected as a product of fractional crystalliza-

tion and gravity sorting of successive crystal fractions. The ratio of mol

per cent (FeO plus MnO)/MgO increases systematically from that in the

ferroaugite (nos. 8 and 9:0.86 and 0.85, respectively) through femag-

hast ingsi te (no.5:1.18) to ferrohast ingsi te (nos.6 and 7:3 '20 and

4.09, respectively). This increase in ratio of Feo to MgO is correlated

with a higher percentage ol quaftz and a higher ratio of normative ortho-

clase to albite in the ferrohastingsite-bearing gneisses.

Hornblende Jrom Younger Gron'itic Rocks

The predominant member of the younger granitic rocks is a horn-

blende-microperthite granite commonly with 20 to 30 per cent quartz'

Hornblende 2 is from this type of rock. The hornblende granite is in part

strongly deformed and recrystallized to a gneiss. Hornblende 3 is from

the hornblend,e to be just in the border zone between femaghastingsite

and ferrohastingsite.There is also a facies of the hornblende granite in which the quartz

content is commonly greater than 27 per cent and the ratio Kzo/NazO is

slightly higher than in the normal granite. The hornblende (no. 4) of this

type of rock is a ferrohastingsite with a relatively high ratio of ferrous

iron to magnesia. (The particular rock from which the analyzed horn-

blende was taken has a lower percentage of quaftz than is normal for

this facies of the granites.) All the chemical and mineralogical character'

o

*

LEONARD

*< r J

A. F. BUDDINGTON AND B. F.

€€ i 6 : O O \ € € € \ O N NN N b O N \ O N N O 4 - I I N \ O

N N N N o O \ O O O O O i O O \q i o \

O O N O N T N O \ O \ O O \ N r x \ O4 4 N - C N - \ O O $ O - I l € O O \ o €. . . . . . t 1

; * - : " o R o o o o o o g n o o

! Q Q ! ? 4 q t \ O € . o O \ O c ) N Q \ O N N O € o O O .N $ € N O N 4 + € ) d C d \ O N a \ O N F N @ €

$ g d S " i c j , j - j - j c ; . i J d o S - e * o i o J o

N

Na

o

< r N < 4 € D \ O O O T O O \ O 4 N < I 4 N C O \ O O \s $ Q N N H O \ o . 1 o O C > € O \ N d r O A < | t O s f o . l O

g : + R - j g - ; - i c j c ; s i c ; d d S ' - S ' j : . j +

c o q , N q ' O q ) o Q - r \ + O n s € O @ N o \ Or d r N € i r + r \ O \ O \ O C ) N \ O b b O O O l r N O \ N

d J ; - i + o , - i - i - i d - i c ;o i N o o 8 o e 9 = o o

o

$ ! 9 Q \ \ \ O i N O o N \ O O @ o . + 4 \ o +S O r c € c ! O c O N O - S O \ € + \ O e - \ O O N

g ' : ; X J o i , j - j * ' o ' d o ' d o g - S ' * ; X ' J s

Q q 4 - \ O < 1 N 4 N O - N \ O 4 4 \ O O . -O X N N - 4 4 N € F € N N @ € O + c ) e * i O

E = " : F i * o . J - j - i o o o o o d - e ' ; N J - i

q j e j ! ! . e € s o \ N n o € o N o o \ i € c o o \ * rq € 4 < i H i O \ + r r o s o O D O N O 4 c ) i - 4

d d ; d . o o - j * J d J J d d S . j g - i * - ; J o

NN

U

il

@

o

+ 1 N r N

o d o i 6 ; - i 6 i

o

: dh \7 N ;! N o

- - c dc d c d i

6 d 6 'O ' t r t lz " . i o o 6F , : F > > Z

c o o " t F N A o N o o . b N O . C O €r 9 0 N € € 4 € 4 N = i r N 4 0

g : d = ; o = j J 6 i d - j - j o o

sQiqc*q?o-5o-a ?li 4, n, tr > d Z v E'E'i-: r. - >

894

6 N :r - h

cd

Q ;

F s , ^ , xv c

a a J

E

. : €i 4 A

H

F XF O

' a

o o

X :

O

z

4

F

H

zF

ts

o

O

./.

tsz.T

ts

vt4Xo

FF2

z!

zo

H

z

a

j

z

L)

E

Q

*.

F

-r

n

'do

E

o

*

GRANITIC ROCKS 89.5

| | l

| | l

<rI r N

o N l

- + N

: - i I

* * *o o 4€ € aO N N

+

O

d

t l l

od

o

E

F

!

tr

HORNBLENDE IN NORTHWEST ADIRON DACK

::::i3r - ; *tl5 gg*g g lll=E o F x

:::5i3ru,u;l$ax i $lt ;= Xs*: ' l . d l N l l -

" Ht li E-E g fi ''irt-\ . / Y A F i ; = d a

r t s : A I t\ @ \ a v v

eRsB^?,^ e" e E EE X*=3:::r#*!:-;II X+5E=N*=: := :?R^L. .€ g X*: : : : ldS_H"*ei "r E T' t

{ ;ag ; ,5 i '

$€FSr?t"^T,E> - [ l ,J - - c j - S ' o - . : g J E ! I E | l '

\ / @ \ r 7 , ' = L >

L -O

D t_J >:(J 9

assxs^e-" ;E 4 X*=6 6 6 d I + 1 9 ^ " * l i " ' ' 2 1 q l l s- - j - d - ; = = i - H = J 3 3 F ' n > - i

a;Y; E3,5 6;

4 . 1. n xX d

. . ' d

- a l

i " ^ O , Y -

! * p- o E : q . . : t ri ; _ E - 8 * ? g g .r F > > =

a q > > O f u i . r A r s X

9 X P 9 ^ t o .6 6 6 o l + t A

: : : ^ - € 6h

N V

\o

cO4 A

. 6

N . l

vO4

z

FI

BF4

zH

O

OF

z

E

a

z

trzo

H

zs

a

F

o

Fl

oEr

N

t,]

Fr

A, F. BUDDINGTON AND B, F. LEONARD

2 G a a a=Bne=a€8x c o = R d o d ;

9 - - 3 = = -N . O i . r 4 \ O N O O c l \

r o € 6 0 Nr 5 0 q

N O €

Q . : l + o O N € - N + o O N c O @ -s € N N - O - 4 S - € € + N

- O C O

" ? a N o ov o - -{ < . ; . i

q l r : Q \ a t € € € F s N N c ) -O 4 € C } O O N € N t s € N - -

o o e o . t o o o o € e d o o

$ a + o s A

N + t o c o N

KT€ S53 :$3 3R S3 :O O i i N O O O O \ O H e O c )

9 t ' c o o on € N - -

N O i o o i

3 3 € 5 g E R R R R 8 : S :O O H O O O O O c ) € t s H C O

c Q D q o qS @ N O O

N s e @ N

s83 3S= R3e 88 S35O O i O N O O O O \ O N i O O

. ? V < i l o d 1O \ O €

6 i + o d . ;

Q Q f a " ? r ? L - o = f - - o - + om € 4 * ' O O O \ O N - - @ . : -o o i * N O O c ) O \ O i H C ) O

' ? 1 9 q o Ns o c o - q

N $ O € O

! 9 \ ? N N q - N N m N o t s \ oO r + h H N O O \ O H o O . b € JO O H N d O O O O 4 N N O O

* - o o : - c ivi , j g- i j aci : a? t l "U

tAEs

896

N V

. ^ 9

€4 A

€

<'1N . l

rt

zo

H

F

zH

O

orrz

E

z!

zH

zt4

a

rl

E

tsl

pgO

-.at)

d

|l

F

HORNBLENDE IN NORTHWEST ADIRONDACK GRANITIC ROCKS 897

istics of this granite, as well as the field evidence, are consistent with the

hypothesis that the more quartzose facies represents a slightly younger

d.ifferentiate of the same magma that yielded the normal granite.

Microcline-rich granite gneiss occurs as sheetlike masses intimately

associated with metasedimentary rocks and amphibolite. The microcline

granite gneiss is interpreted as in large part the product of modification,

granitization, and migmatitization of metasediments and amphibolite by

potash-rich solutions. The hornblendic facies of the microcline granite

gneisses are always associated with included layers, schlieren, and dis-

integrated relics of amphibolite. The hornblende ranges from femaghast-

ingsite to ferrohastingsite. The variation in composition probably de-

pends in part upon the degree of modification by granitizing solutions of

the hornblende derived by incorporation from amphibolite.

OPrrcnr AND CHEMrcar Dera

Optical Properties oJ Sorne Ad,irondack Hornblend'es*

Indices of Refraction

The indices of refraction were determined in sodium light by the im-

mersion method, using freshly standardized liquids varying by intervals

of 0.002 in the range from 1.660 to 1.700, and by slightly less than 0.005

in the range from 1.700 to L725. The temperature at which the measure-

ments were made was closely controlled.The indices a and .y were determined on cleavage flakes parallel to the

{010} parting. The index B was determined on rare grains perpendicular

to an optic axis, or on very rare grains perpendicular to Bxu'

Five separate determinations of a, B, and 7 were made for most horn-

blendes, though the number of determinations ranged from 4 to 11' For

hornblende 4, a was determined with exceptional precision; total and

partial birefringences were measured. by H. H. Hess, using a technique

developed for the study of pyroxenes (Hess, 1949); and the values for

B and,7 were calculated from a and the partial birefringences'

The reported values for indices of refraction are thought to be the best

approximations possible at this time. Two factors seriousiy affect the ac-

curacy of the determinations:1. Pure hornblende concentrates from a single hand specimen are

slightly variable in composition. Because of weak absorption parallel to

X, o ca.t usually be determined with greater accuracy than B or 7; and

on a given grain the value of a can be determined in sodium light with an

x To keep within the page limits imposed for this issue of the journal, it was necessary

to delete a section on crystil form anJ cleavage of the hornblendes and to condense the

sections on measurement of indices of refraction, 2V, and extinction angle'

898 A. F. BUDDINGTON AND B. F. LEONARD

error of 0.001 or less. However, the range in a for several grains in thesame mount may be as m.uch as 0.003. A similar range was observedfor the values of B and ,y. (But see factor 2, just below.)

2. Absorption parallel to Y and Z is so strong that the determinativeerror in B and 7 may be slightly greater than 0.001.

Birefringence

The values for total birefringence reported just below the indices of re-fraction in Table 2 were determined, as usual, by dif ierence. Because ofthe range in a and 7, reflecting variable composition, it was feared thatthese values for total birefringence might be slightry in error. To checkthis possibility, separate birefringence determinations were made bymeans of a Berek compensator for all hornblendes except nos. 2 and 3.The resuits are given at the bottom of rable 2. For hornblendes, exceptno. 4, described in the preceding section, the measurements were made onordinary thin sections. The thickness of a quartz grain adjacent to, or onlyone grain removed from, a suitable hornblende was determined by meansof the Berek compensator. The total or partial birefringence of the horn-blende was then determined. The measurements for hornblendes 5 and6 were made on the microscope stage, using X-Z sections of quartz andsuitably oriented sections of hornblende. The measurements for horn-blendes 1 and 7 were made on a universal stage according to the techniquedescribed by Emmons (1943, pp. 172 IB2).

The agreement between birefringences determined by immersion andby measurement of retardation in ordinary thin sections is generallygood' (See table 2.) At least the direct determination of birefringenceserves as a check against serious errors in the relative values of theindices of refraction of a given hornblende. For example, 7 minus a forhornblende 5 seemed very low relative to the total birefringence of theother hornblendes. However, direct measurements of the partial bire-fringences of this hornblende confirmed the results of the immersionwork.

Opl ic Axia l Angle

The optic axial angle was measured in thin section on the universalstage, using a number of grains normal or nearly normal to Bx". Thisangle is reported in Table 2 as 2Y^.o,. under the best of conditions, theprecision of measurement on these hornblendes ranges from f" to 2". Therange of values reported for 2v^"u". in Table 2 is due in part to slightvariation in composition of the hornblende, from grain to grain, and inpart to unavoidable errors in measurement. strong absorption parallelto Y and z makes proper orientation of sections subnormal to

-Bxu ex-

HORNBLENDE IN NORTHWEST ADIRONDACK GRANITIC ROCKS 8q9

ceedingly difficult on the universal stage, and the resulting determination

of 2V is therefore suspect. In addition, total reflection from the surface

of the grain may occasionally be confused with one extinction position.

Dispersion

The dispersion of the optic axes is inclined. It is always distinct or

strong for one optic axis; it is less pronounced for the other, even when

apparent dispersion is reported as strong for both axes (e.g., hornblende

1, Table 2) . Dispersion was determined qualitatively by examining many

optic axis figures for each hornblende. It was not possible to assign the

relative intensity of dispersion to optic axes A or B, nor was it possible

to measure 2V in red light and in blue light. A correct statement of the

true optic axial dispersion for hornblende 1, and perhaps for hornblendes

5 and 6, would of course depend on such measurements'

Extinction Angle

The extinction angle Z /r,c was measured on the microscope stage, using

hornblende sections parallei to the optic plane. The values reported in

Table 2 are averages of repeated determinations made on a number of

suitably oriented grains. Thin sections, rather than immersed fragments,

were used. Because of strong absorption parallel to z, it is difficult to get

the correct extinction position ol Z, as well as to see the trace of the

cleavage whose zone axis is c. Moreover, the cleavage trace observed on

sections parallel to the optic plane is moderately to highly irregular.

Consequently, the extinction angle measured on a single grain may vary

by as much as 9o. A range of 3" to 4o is common. Probably relatively

Iittle of this variation is due to compositional variation in the hornblende.

Owing to the diffi.culty of determining extinction positions and orient-

ing cleavage planes on the universal stage, U-stage measurements of

zAc for hornblende 1 showed a greater range (* 7o) than microscope-

stage measurements made on the same grains cut parallel to the optic

plane. U-stage measurements of ZAc in re-oriented random sections of

hornblende 1 were even less reliable, showing a range of I 10". Measur-

ingZ/\cby observing the extinction position of X, and then rotating 90"

on the outer vertical axis, may have increased the accuracy of some de-

terminations by |o or 1".At present, there seems to be no reliable method for accurately de-

termining Z/x,c on the hastingsites described in this paper' Leonard pre-

fers to measure ZAc onX-Z sections on the microscope stage, if necessary

checking the orientation of the same grains on the universal stage and

checking to see that c is truly the zone axis for the observed cleavage

traces.

A. F, BUDDINGTON AND B. F. LEONARD

Pleochroism and Absorption

The colors reported for X, Y, and Z are those observed in thin sectionshaving an average thickness of 0.020 to 0.025 mm. (These thicknesseswere determined by measurements of retardation in suitably orientedqtartz grains.) In thin sections 0.030 mm. thick, X is pale but Y and Zfor most hornblendes are very dark or almost black, the body color ofhornblendes seen in hand specimen. Crushed hornblendes immersed inoil transmit almost no light parallel to Y and Z unless the fragments aresmaller than about 200 mesh. For most hornblendes, Y and Z rcmainvery dark, though appreciably colored, for fragments as small as -400,

*600 mesh.The determination of the color of Y is sometimes difficult if the horn-

blende has strong dispersion. A section a few degrees subnormal to anoptic axis will include more emergent red light or more emergent blue,depending on the orientation of the grain. A relatively small tjlt will thusproduce a substantial change in the observed color of Y, which is actuallyY'. The difficulty is obviated, of course, if the sections are truly normalto the optic axis or acute bisectrix.

The absorption indicatrix of the hornblendes coincides with the opticalindicatrix. This relation is quite difierent from that obtaining amongcertain common clinopyroxenes, especially among members rich in Fe"'(Hess, 1949).

General Relations of the Ad.irondack Hornblendes

All the Adirondack hornblendes in granitic rocks for which data areavailable show a noteworthy amount of chlorine. There are but fewanalyses of hornblendes in the literature that give the per cent of chlorine.If this is to be taken to indicate that chlorine is minor in amount, thenthe Adirondack hornblendes are exceptionally rich in this element. It ispossible, however, that chlorine occurs in significant amounts in somehornblendes in which it has not been determined. A ferrohastingsitefrom the rapakivi granites of Finland, described by Sahama (1947), has0.51 per cent Cl and 1.06 per cent F. A pargasite from the Tiree marbleof the Hebrides, described by Hallimond (1947), has 0.46 per cent Cl and0.16 per cent F. Hall imond (1947, pp.237-238) notes that the amphiboleapproaches hastingsite in composition. A ferrohastingsite described byKrutov (1936) and named by him dashkessanite,has 7.24 per cent CI. Afemaghastingsite from garnetiferous amphibolite of the central Adiron-dacks, New York, described by Buddington (1952, p. 42, no. 9), has0.63 per cent Cl and only 0.08 per cent F. A comparison of hornblendesfrom Adirondack amphibolites (Buddington, 1952, pp. 42 and 53) alsoshows that the total alkalis are higher in hornblendes having significant

HORNBLENDE IN NORTHWEST ADIRONDACR GRANITIC ROCKS 901

amounts of F or Cl than in those having only a slight amount of thehalogens.

Both in the granitic rocks of the Diana-Stark complex and in theyounger granitic rocks, the ferrohastingsite hornblendes carry a veryslightly higher percentage of total alkalis than the femaghastingsites.Also, in each of the two rock series there is a systematic decrease in theper cent of total OH, F, and Cl as the ratio MgO/FeO decreases.

Hornblendes of similar chemical composition occur both in primaryigneous rock and in the gneissic equivalents.

A pargasitic variety of hornblende is found in a thin layer of thoroughlyrecrystallized amphibolite enclosed in the granite from which hornblende2 was concentrated. Pargasite from the amphibolite contains 0.91 percent F and 0.03 per cent Cl (Buddington, 1952,p.42, no. 1). This con-trasts with 1.50 per cent F and 0.37 per cent Cl found in the femaghast-ingsite (no. 2) of the granite. The femaghastingsite (no. 2) of the granitehas a much higher ratio of

FeO * MnO_==- : 1 .89

than the pargasite of the amphibolite, which has

F e o * M n o : 0 . 7 8 .

Msoas one would expect.

The main purpose of this investigation has been to define the chemicalcomposition and optical properties of hornblendes from granitic rocks ofthe northwest Adirondacks, and to discuss their petrologic significance.A secondary goal was to correlate these data and the previously pub-lished data on similar amphiboles, in order to increase our understandingof the hastingsite group. So far, a reasonably precise correlation has notbeen achieved, owing mainly to the extreme complexity of the hastingsitegroup and to the lack of reliable and essentially complete chemical andoptical data on its members. The lines of attack recently employed byFoslie (1945) and Sundius (1946) have been especially fruitful, but theneed for additional data is great.

Rnlnnpxces

Brr,t-tNcs, Manuxo (1928), The chemistry, optics, and genesis of the hastingsite group ofamphiboles : Arn. M ineral., 13, 287 -296.

BunotNctoN, A. F. (1939), Adirondack igneous rocks and their metamorphism: Geol. Soc.Amer. , Mem.7, 354 pp.

-=- (1948), Origin of granitic rocks of the northwest Adirondacks, in Gilluly, James,chm., Origin of granite: Geol. Soc. Amer., Mem.28, 2l-43.

902 A. F. BUDDINGTON AND B, F. LEONARD

- (1952), Chemical petrology of some metamorphosed Adirondack gabbroic, syeniticand quartz syenitic rocks: Bowen volume, Am. Jour. Sci..,37-84.

Euuoxs, R. C. (1943), The universal stage: Geol'. Soc. Amer., Mem.8,205 pp.Foslrr, SrrrNan (1945), Hastingsites, and amphiboles from the epidote-amphibolite

facies : N orsk geol. liilsshr., 25, 7 4-98.HallruoNn, A. F. (1947), Pyroxenes, amphibole, and mica from the Tiree marble (with

chemical analyses by C. O. Harvey): Mineralog. Mag.,28,230-243.Hnss, H. H., (1949), Chemical composition and optical properties of common clinopy-

roxenes, Part I : Am. Mineral,., 34, 621466.Knurov, G. A. (1936), Dashkessanite-a new chlorine amphibole of the hastingsite group:

Acad.. Sci.U.R.S.S. Btill,., ser. geol.,34l-373. (Cited in M'inerol'og. Abs., 1937,6' 438.)Senaur, T. G. (1947), Rapakivi amphibole from Uuksunjoki, Salmi area: Comm. geol.

Finlande Bull. l4O, 159-162.Suxorus, Nrr.s (1946), The classification of the hornblendes and the solid solution relations

in the amphibole group: Soeri.ges geol. Untlersi)hning, ser . C , no . 480, 36 pp.