THE AMERICAN MINERAI,OGIST, VOL. 48, NOVEMBER-DECEMBER, 1963

NICKELIFEROUS SERPENTINES, CHLORITES, ANDRELATED MINERALS FOUND IN TWO

LATERITIC ORES

J. W. MoNroYA AND G. S. Baun

ABsrRAcr

The nickel-bearing serpentines, chlorites, and related mineral species found in laterite

oresfrom Californiaand New Caledonia were identified by detailed mineralogical, optical,

chemical, *-ray difiraction, difierential thermal, and infrared spectra analyses. Electronmicrographs were prepared to define the morphology of each variety. The principal ser-

pentine minerals were lizardite, clino-chrysotile, and antigorite. The minerals contained

from 0.3 to 5.3 pct nickel. Electron micrographs of the lizardites showed tubular particle

forms in some samples and minute plates in others.Clino-chrysotile occurred chiefly as a component of natural mixtures with lizardite,

antigorite, or chlorite. Clino-chrysotile exhibited a variety of tubular habits ranging from

long splintery tubes and fibers to relatively short, broad, multiple tubes. Additionally,

pure orthochrysotile was isolated and identified.

Nepouite, garnierite, nickel-bearing varieties of penninite, fibrous antigorite and septe-

amesite also were identified, isolated and described.

INrnoouctoN

Californian nickeliferous-laterite ores have been described by Jenkins(1953, 1954). I{owever, l i tt le work has been done to identify the ser-pentine minerals present in these ores. Extensive geological studies weremade on the New Caledonian laterites by LaCroix (1942), deChetelat(1947), and Cail lbre and Henin (1960). I{owever, there appeared to beiittle agreement among these authors as to the nomenclature of theminerals present. In addition, non-nickel-bearing serpentines have beenstudied extensively by Faust and Fahey (1962).

This paper identifies, classifies and gives detailed descriptions of theoptical, chemical and physical properties of the nickel-bearing serpentineand related minerals found in Californian and New Caledonian lateriticores.

The serpentine nomenclature used in this paper is that of Whittakerand Zussman (1956), who classified the serpentines into three maingroups: Chrysoti le, l izardite and antigorite. Two major forms of chryso-ti le, clino-chrysoti le and ortho-chrysoti le, were recognized. Both formsexhibit a tubular morphology but are distinguished by differences intheir o-ray diffraction patterns. The name lizardite was proposed for aone-layer ortho-serpentine mineral. The name antigorite was used toidentify a serpentine mineral having platey morphology and a larger unitcell than chrysotile and lizardite.

The related minerals in the ores, penninite, septeamesite, nepouite

t227

1228 T. W. MONTOYA AND G. S. BAUR

and garnierite, were identified on the basis of chemical analyses andknown *-ray difr.raction data. The prefix "septe" was proposed by Nel-son and Roy (195a) to distinguish chlorite minerals having a series ofbasal ;r-ray reflections due to a 7 A interplanar spacing from more com-mon chlorite which is characterized by a 14 A periodicity.

Sllrprp DBscnrptroNs

Materials for this study were selected from Iarge representative lots ofore. Samples comprised minus ]-inch serpentine fragments and limoniticfines.

The laterit ic ore from Humboldt County, California, contained about15 pct serpentine minerals including a trace of garnierite, 55 pct limonite,and over 30 pct forsterite and hypersthene. Small-to-minute quantit iesof maghemite concretions, chromite and biotite also were present.

New Caledonian lateritic ore was comprised of 60 pct serpentine andchlorite minerals including minute quantities of nepouite and garnierite;25 pct l imonite; and 15 pct actinolite, enstatite, forsterite and maghemiteconcretions. Traces of anorthite. tremolite asbestos and chromite wereidentified.

Lanoneronv IsvBsrrcarroNs

Samples of the lateritic ores were prepared for mineral identificationby self-attritioning and washing to remove friable limonitic fines, whichwere discarded. Thereafter, the coarse fraction of each ore was handsorted into various groups according to color and physical appearance.Each group then was crushed, screened and separated into appropriatespecific gravity fractions from which specimens of relatively pure serpen-tine and related mineral species, as well as natural mixtures of theseminerals, were selected for detailed study and analyses.

Mineralogical studies: The major serpentine mineral found in the twoores was lizardite. The other serpentine and related mineral species oc-curred in minor-to-trace quantities, generally as natural mixtures of twoor more varieties. The distinguishing physical and optical properties ofthe serpentine and related mineral varieties found in the two ores arepresented in Table 1.

Specimens obtained from the Californian deposit contained a nickel-bearing lizardite and small quantities of clino-chrysotile and fibrous an-tigorite. Minute grains of garnierite also were identified.

Specimens obtained from the New Caledonian deposit consisted

LATERITIC SERPENTI N ES AN D CTI LORITES

Tasrn 1. Oprrc,lr erqo Pnvsrclr- Pnoprnrms or SnntnNtttns, Ctrr-onrrns,.nNl Rnr,nrpo Sprcrrs

1229

Mineral Color Refractive index Habit

PlatesDo.

Do.PIates

Do.

FibersDo.

Cryptocrystalline

Plates

Fibers

Cryptocrystalline

Do.

Lizard.iteCaliforniaNew Caledonia

Clino-chrysoti.l'eCaliforniaNew Caledonia

Orl,ho-chrysotil,eNew Caledonia

Anti.gori.te

CaiiforniaNew Caledonia

Related, speciesNew Caiedonia

septeamesiteNew Caledonia

penniniteNew Caledonia

nepouiteCalifornia

o q r n i e r i f p

New Caiedoniagarnierite

Ye1low-greendo.

Light- to dark-greenLight-green

Gray-green

WhiteLight- to dark-green

Light-green

Yellow- to dark-green

Bright- to blue-green

Light- to yellow-green

do.

r . . ) / J1 .575-1 . 580

1 570-1.5801 . 565-1 .575

1 .570-1 .575

1 . 5 6 51 . . 5 6 5 1 . 5 7 5

1 . 540-1 .560

I .590

1.62A1 .630

1 . 545-1 .570

mainly of nickeliferous lizardite. Nickel-bearing clino-chrysotile andpenninite were present in minor quantities generally as natural mixturesin combination with each other andf or with lizardite. Ortho-chrysotile'septeamesite, nepouite and garnierite ociurred in small amounts as iso-lated grains. A few grains of impure antigorite were identif ied.

Chemical studies: The chemical analyses of the serpentine minerals arepresented in Table 2. The percentages given in this table represent aver-

age values obtained by analyzing a number of fragments. Similar chem-ical analyses of the New Caledonian chlorites, nepouite and garnierite

are shown in Table 3. The chemical analyses of the serpentines agreefairly well with the l iterature (Faust and Fahey, 1962), except for thesubstitution of variable amounts of nickel for magnesium. The analysis ofnepouite is in close agreement with that of nepouite published byAlekseeva and Godlevsky (1937). Garnierite, according to Dana (1914)'

has a variable composition, especially with respect to the mutual re-placement of nickel and magnesium. This variability of chemical com-

1230 J, W. MONTOYA AND G. S. BAUR

Taer,B 2. Cnrurc,tr Atar,vsns ol SnnprurrNB MrNnnar,s

Al2oa

Analysis, pct

Mgo CrzOr

Mineral

Lizard.iteCaliforniaNew Caledonia

Clino-ehrysotileNew Caledonia

Antigorite

California

SiOr

4 0 83 8 . 3

4 1 . 3

39 .6

0 . 2. o

1 . 0

FezOr

7 . 26 . 8

3 . 4

5 . 9

FeO

n . d 2

34.33 3 . 3

3 4 . 4

39.9

n.d .2

0 . 2

n d . 2

2 . O+ . 3

. J

1 Difference between loss on isnition at 4000 and 9000 C.2 Not determined.

position also is reflected in the variabil ity of the optical character (Table1 ) .

X-Ray d.ifraction stuilies: Identification of the serpentines, chlorites andrelated species was based in part on f-ray difiraction data. Lizardite,clino-chrysoti le, ortho-chrysoti le and antigorite were identif ied usingr-ray data. compiled by Whittaker and Zussman (1956). Septeamesite,penninite, nepouite and garnierite were identif ied by comparison withASTM r-ray dif iraction data.

T.lern 3. Cnnurclr ANlr,ysns ol Nnw Cer-nnoNraN Cnr-onrms lNo Rnlarnrr Mrunnar,s

Analysis, pct

Mineral

SepteamesitePenniniteNepouiteGarnierite

SiOz

30 .93 2 . 73 3 . 846.7

AlzOa

2 6 . 7L+. . )

4 . 1< 1 . 0

Fe:Oa

0 93 . 81 . 31 . 4

FeO

n . d . 2

2 . 5n . d . 2

n . d . 2

Mgo

2 1 . 429.61 3 . 519.9

CaO Cr:Oa

trace0 . 3

. 1n . d 2

Nio

3 . 63 . 2

34. 814 .5

LOI

4000 c. 9000 c1

n .dn .d .

4 . 8 1 0 . 61 . 7 1 1 . 1r . 6 1 0 . 63 . 0 1 1 . 2

tracet 6

I Difierence between loss on isnition at 4000 C.2 Not determined.

I,A7' ERITI C SERPENTI N ES AN D CH I,ORITES 1231

X-ray diffraction data for the serpentines, chlorites, nepouite andgarnierites are presented in Tables 4 and 5. The specimen of Californiagarnierite used was contaminated with serpentine and quartz. Many ofthe peaks in the r-ray pattern shown are due to or have been intensified

D - 7 4 6 - S L

Frc. 1. Smoothed powder diffraction patterns for serpentines, chlorites, nepouite, and

garnierite. (1) California lizardite, (2) New Caledonia lizardite, (3) New Caledonia clino-

chrysotile, (4) New Caledonia orthochrysotile, (5) California antigorite, (6) septeamesite,(7) penninite, (8) nepouite, (9) New Caledonia garnierite.

2

7.

8.

9.

75 70 65 60 55 50 45 40 35 30 25 20 15 lO

| | | | | l,lu,l.n,.L, I | | | I

1232 J. W. MONTOYA AND G. S. BAUR

by the presence of the serpentine impurity in the sample. If the reflectionssuspected as due to the presence of serpentine are ignored, the data agreefairly well with that of ASTM card No. 2-0060 as well as with that ofAlekseeva and Godlevsky (1937). Copper Ka radiation was used. Thediffractometer patterns are reproduced as Fig. 1.

Tenrr,4. X-Rey DrlpnecrroN Dera lon Lrzenorrns en.o Cunvsolr,rs

Lizardtte

dA

New Caledonia

Clino-chrysotileNew Caledonia

Ortho-chrysotileNew Caledonia

7 .25 004.55 452.605 503.65 1002.499 852.460 602.336 352.149 10r . 9 7 1 2 01 . 8 1 6 5 11.723 1511.64 t 151.538 6s1.509 301.310 251

7 . 1 94 . 5 3? o n

3 .632.4932.4532.1541 .7921 .5401 .504I . 310

7 . 2 54 . 5 53 . 9 13 . 6 52.499

2.145r . 7 8 9l . J J O

r .5021 .310

7 . 2 54 . 5 72 5833 . 6 62.4862 . M 02.0921.8231 . 7 3 91 . 5 3 41 . 4 7 0

| 1 1 q

852525

1004065I J

10l . )

4510

20

100155

60J.)

20155

2010101

7545

<5100706020104020201

I Broad peak.

Diferential thernr.al analysis stutlies: Differential thermal analyses weremade on selected serpentine and chlorite specimens. The curves areshown in Fig. 2. The general shape of the curves agreed with those ob-tained on similar minerals by Faust and Fahey (1962), Nelson and Roy(1954) and Brindley and Ali (1950). No difierential thermal data wereavailable on nepouite. The samples were heated 12o C. per minute in anair atmosphere. In all samples, the differential thermal analyses showeda strong endothermic reaction between 600o and 750o C., which was dueto dehydration and destruction of crystal structure. Nickeliferous lizard-ite, clino-chrysoti le, septeamesite and penninite showed evidence of anadditional weak endothermic reaction near 800' C. AII varieties testedexhibited a strong exothermic reaction due to the formation of forsterite

LATERI:TIC S ERPENTI NES AN D CH LORITES

Tenr,n 5. X-R.ty Drllnlcrrow Dera ror Axrrconrrn, SnrtoeursrrE,PnNurNr:rn, Nneouttn, .tNo G.lr.mrntrrB

1233

AntrgoriteCalifornia

Septeamesite,New Caledonia

Penninite,New Caledonia

Nepouite,New Caledonia

Garnierite

California New Caledonia

l/IndAdA (l.AI/IidAI/lodA

7 . 1 94 . 5 9

4 . 1 34 . 0 03 6 02 5272 . 4 2 12 2tO2 1541 . 8 1 6

1 . 7 3 21 . 5 6 21 . 5 3 61 . 5 1 31 .5021 . 4 7 8

1 .450L J l 5

951 0

1 05

10030t .1

< 51 05

5101 0555

5

7 . 2 5

4 . J J

3 . 6 2

2 . 6 4 2

2 . 4 7 9

2 149

1 0 . 4

6 . 45 04 . 6 100r

7 . 1 9 8 0

4.60 403 59 1002 9 6 5

2 .650 502. 583 55

2.3842 . 2 5 7

2 0091 886

1 7261 . 6 6 51 .569

t .5021 .405

80I J

l . )

1025l 5

6020l 5

20t 5

5

1 1 2 5 57 1 3 9 04 . 7 4 7 04 . 6 2 1 03 . 5 7 1 0 0

2 838 25

2.583 202.540 302.440 252 . 3 7 8 1 52 252 10

2.004 251.886 10t . 8 2 3 5t . 7 4 2 51 . 6 6 0 51 . 5 6 4 1 51 . 5 4 1 2 51.504 10t . 4 t 6 51 . 3 9 6 1 51 3 1 8 1 0| 290 101 2 2 3 5

100r7521010

100r

1C0

35100

55r65r651

3.68 502

3 22 10r2 .65 7512 45 7Sl

40

60r

<51, '101

100r'2100r,2

3 . 2 42 6502 . 4 6 0

| 7 a o

1 5 3 11 . 3 1 5

t . 5291 .500

6030

25r

r Broad peak.r Peaks due to or augmented by the presence of serpentine minerals.

andf or enstatite between 750" and 850o C., with the exception of NewCaledonian septeamesite and nepouite, which exhibited weak reactionsin this temperature range.

Thermal reaclion stud.ies: Supplemental studies were made to correlatethe reactions detected by DTA with phase changes that occurred in theseminerals upon heating. Individual samples were heated in air for 30 min-utes at various temperatures ranging from 500o to 1,000" C. The heat-treated samples then were examined by r-ray difiraction analyses toidentify the different phases formed. The pertinent findings are sum-marized in Table 6.

Temperatures at which the serpentine and chlorite minerals decom-posed and then recrystallized to form forsterite varied. AII minerals

1234 T. W, MONTOYA AND G, S. BAUR

studied however, formed enstatite between 750o and 850' C. Except forantigorite all heat-treated minerals exhibited an amorphous phase be-fore the formation of forsterite. Antigorite apparently decomposed simul-taneously with the formation of forsterite. Septeamesite transformed. to

D-745 -SL

Frc. 2. DTA curves for serpentines, chlorites, and nepouite. (1) California lizardite,(2) New Caledonia lizardite, (3) New Caledonia clino-chrysotile, (4) California antigorite,(5) septeamesite, (6) penninite, (7) nepouite.

sapphirine in addition to forsterite between 750o and 800o C., and toforsterite, enstatite and a spinel-type structure above 800" C.

The chlorites, when heat treated, retained or developed a symmetryassociated with the 14.7 Aand 2.8 A interplanar spacings. In heat-treatedpenninite, the chlorite structure collapsed except for this symmetry.The 14.7 A and 2.8 A reflections increased in intensity as the sample was

300 ztoo 500 600 700 800 200Tem pe ro lure, oC

LATb:,RITI C SERPENTI N ES A N D CH LORITES r235

Tanm 6. PnasB CulNcrs oN HBauNc Pnooucnl rN SnnpeNTrNns eNn Cnr-onrtrs

Temperature of phase change, o C

Mineral Decomposition ofserpentine Iattice

Forsteriteformation

LizardileCaliforniaNew Caledonia

Clino-chrysotileNerv Caledonia

AntigoriteCalifornia

ChloriteNew Caledonia

septeamesite

New Caledonia- p - - i - i t p

5.s0-600550-600

550-600

600-650

700 750

650 700

750-800750-800

750-800

800-850

800-850

750-800

heated unti l forsterite formed (about 750" C.), at which temperature theydisappeared. The high temperature form of septeamesite, represented byweak reflections due to 14.7 A and 2.8 A interplanar spacings, appearedat about 500' C. These peaks also disappeared with the formation offorsterite.

Infrared, studies: Infrared absorption spectra were recorded on thenickeliferous serpentines, chlorites, nepouite, and garnierite as an aid indistinguishing the different varieties. The spectra for the 9 to 11 micron-wavelength range are presented in Fig. 3.

Samples were mixed with potassium bromide and hand ground underalcohol to prevent lattice destruction and then pressed into disks. lVleas-urements were made using sodium chloride optics.

Although the serpentines and chlorites gave somewhat simiiar ab-sorption spectra, dif ierences in the position, shape, and intensity of thepeaks enabled the varieties to be distinguished from one another. The re-sults agreed generally with those of Brindley and Zussman (1959) andTuddenham and Lyon (1959).

Electron microscope stud.ies: The morphology of the serpentines, chlorites,nepouite and garnierite was determined by the electron microscope.

1236 T. W. MONTOYA AND G, S. BAUR

D - 7 4 3 - S L

Frc. 3. Infrared curves for serpentines, chlorites, nepouite, and garnierite. (1) Cali-fornia lizardite, (2) New Caledonia lizardite, (3) New Caledonia clino-chrysotile, (4) NewCaledonia ortho-chrysotile, (5) California antigorite, (6) septeamesite, (7) penninite, (8)

nepouite, (9) garnierite.

l\ Lizard.itesCalifornian lizardite exhibited a tubular morphology, whereas New

Caledonian Iizardite consisted of plate-like particles similar to those ofIizardite from Snarum, Norway, photographed by Zussman et al'. (1957).

Comparison of the r-ray pattern of the California lizardite with the r-raydata on chrysotile compiled by Whittaker and Zussman (1956) demon-strates the tubular California lizardite is neither ortho- nor clino-chrysotile. Although the California lizardite could be mistaken for poorlydeveloped antigorite, its tubular habit and the DTA and infrared datarule out this possibility.

3

4

i l 9

WAvELENGTH, m ic rons

LATERI TI C SA,RPENTI NES A N D CH LORITI]S L L J I

2) Clino-chrysotileRelatively pure clino-chrysotile and clino-chrysotile-antigorite mix-

tures in New Caledonian samples occurred as relatively long, thinsplintery tubes and fibers. Some of the fibers appeared to have curlededges. Clino-chrysoti le mixed with penninite or with l izardite occurred asthin splintery tubes and fibers and as relatively short, broad multipletubes (tube-in-tubes). The multiple tubes consisted of progressivelyIarger tubes similar to a telescope, or of a broad tube enclosing a longer,thinner tube that projects at both ends.

3) Ortho-chrysotil,eThe ortho-chrysoti le from New Caledonia exhibited a tubular mor-

phology similar to the New Caledonian clino-chrvsoti le, but the tubeswere somewhat shorter.

4) AntigoritesCalifornian and New Caledonian fibrous antigorites occurred as broad

Iaths.

5) Septeamesite, penninite anil nepouiteNew Caledonian septeamesite, penninite, and nepouite occurred as

plates. Septeamesite occurred as minute, irregularly shaped platey par-ticles. Penninite plates were large and broad. Nepouite plates were some-what smaller than the penninite plates and appeared to be hexagonal inoutl ine.

AcrwowlBocMENTS

The authors wish to thank B. H. Clemmons, Jr., Research Director,and the stafi of the Salt Lake City Metallurgy Research Center of theBureau of Mines, for their assistance, especially that of R. G. Anderson,for the differential thermal analysesl K. R. Farley, for the infrared spec-tral and M. R. Howcroft, for the chemical analyses.

RnprnrncnsAr.txsmve, E. F aNn M. N. Golr.avsxv (1937) X-ray studies of nickel hydrosilicates.

Mem. Soc. Russe Minera). , Ser. 2,66,51-106.BnrNor.rv, G. W. arro S. Z. Ar-r (1950) X-ray study of thermal transformations in some

magnesian chlorite minerals. Acta Cryst.,3, 25-30.

J. ZussueN (1959) Infrared adsorption data for serpentine minerals. Am.Mineral.44, 185-188.

C,ur-r,inn, S. amn M. S. HnNrN (1960) Etude min6ralogique de certains mindrals de nickeldits "nickel coocolat. " S ilicate I ndustrin l s, 25, 29 3-296.

D,m.l, E. S. (1914) A System oJ Minerology. John Wiley & Sons, Inc., 6th Ed., New york,

N. Y., pp. 67e677.on Cnnrnlet, E. (1947) La genbse et l'evolution des gisements de nickel de la Nouvelle-

Caledonie. S oc. Geol France. Btdl. ser. 5, 17, 105-160.

1238 J. W, MONTOYA AND G. S. BAUR

F.tusr, G. T. .tNo J. J. F.lnav (1962) The serpentine-group minerals' U' S' GeoI' Suney

ProJ. Paper 384-4.

JurrrNs, Or,rr P. (1953) Serpentine in California. Minerol InJo. Sent., State oJ Col'iJornia,

6 ,74 .- (1954) Nickel in California. Mineral InJo' Sera., Stote of caliJorni'a,7' l-5'

L,r Crox, A. (Ig42) Les peridotites de Ia Nouvelle, caledonie; Ieurs serpentines et leur

gitesdenickeletde cobalt; les gabbros qui les accompagnent. Aco.d. sci. Paris Mem.

66, I-143.NnrsoN, Bnucn W. er.ro Rusruu Rov (1954) New data on the composition and identi-

fication of chlorites. Seconil Nattr. ConJ. Cl,ays Clay Minerals, Nat'|, Acad. Sci.. Pub.,

Pp.327,335-348.Tuntrrnmn, w. M. er.ro R. J. P. LvoN (1959) Relation of infrared spectra and chemical

analysis in the chlorite mineral seies. AnoJ. Chem.3lr 377-380'

wnrrrernn, E. J. W. lNn J. Zussur.N (1956) The characterization of serpentine minerals

by X-ray diff ra cIion. M iner al,. M a g. 3I, 107 - 126.

zussMAN, J., G. W. Bnrnor.nv AND J. J. Courn, (1957) Electron diffraction studies of

serpentine minerals. A m. M iner ol. 42, 133-153'

Manuscript receioed, A pril 8, 1963; accepted' Jor publi'cation, Jul'y 2, 1963'