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High-resolution infrared spectra, physical properties, and micromorphology of serpentines
Applied Clay Science 16 Ž2000. 73–85
High-resolution infrared spectra, physical properties, and micromorphology of serpentines J.L. Post
a,)
, L. Borer
b
a
b
California State UniÕersity, Sacramento, CA, USA Department of Chemistry, California State UniÕersity, Sacramento, CA, USA
Abstract Separate serpentine minerals may be identified by near infrared ŽNIR. spectra using remote sensing or portable field devices, and identified in the laboratory by NIR and mid-infrared spectra, but X-ray diffraction ŽXRD. procedures are necessary for rapid identification of serpentine mineral mixtures. Compacted serpentine aggregate material is very stable with a density of about 2400 kgrm3 having an internal friction angle of about 328 with weak cementation. Non-fibrous clinochrysotile, the most common serpentine mineral in California deposits, consists of densely ˚ diameter, which are too short to be considered asbestiform. The packed tubules from 600 to 700 A Picrolite fibers are brittle and too large to be asbestiform. q 2000 Elsevier Science B.V. All rights reserved. Keywords: serpentine; clinochrysotile; lizardite; picrolite; fibrous minerals; IR spectra; X-ray diffraction
1. Introduction The California State mineral is serpentine, commonly found in most northern California counties and widely used as crushed aggregate material for construction purposes. Of the numerous small chrysotile asbestos mines, only one remains in operation. The purpose of this study is to show methods of identification of distinct serpentine minerals by infrared spectra involving remote sensing and laboratory testing methods, the results of standard physical tests for construction, and to show the micromorphology of the dominant non-fibrous clinochrysotile serpentine and of picrolite. )
Corresponding author. Vector Engineering, Grass Valley, CA, USA. Tel.: q1-530-478-0542; Fax: q1-530-272-8533 0169-1317r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 1 3 1 7 Ž 9 9 . 0 0 0 4 7 - 2
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
The combination spectral bands, with overtone bands of serpentine were given by Hunt et al. Ž1973. and the dominant combination band assignments by Hunt Ž1977. and Hunt and Ashley Ž1979. . This was followed by high-resolution reflectance studies of chlorites and serpentines by King and Clark Ž1989.. The main purpose of these studies was for remote sensing and land surface mapping. Serpentine mineral identification, with chemical analyses, of samples from California was given by Post et al. Ž1999.. Nearly pure specimens of antigorite, clinochrysotile, and lizardite, from a collection of more than 100 analyzed specimens, were chosen for preparing infrared spectra.
2. Materials and methods 2.1. Materials Two specimens of lizardite were obtained, one from a road cut north of Shingle Springs, California, Lizardite 11, and the other from a road cut east of Georgetown, California, Lizardite 51. Specimens of fibrous clinochrysotile were from south of Lake Berryessa, California, Clinochrysotile 22, and from south of Dawson City, Yukon Territory, Clinochrysotile 23, and two specimens of non-fibrous clinochrysotile were from a roadcut on State Hwy 3 north of Weaverville, California, Clinochrysotiles 95 and 96. The Lizardite–Orthochrysotile specimen 42 was from a roadcut northwest of Washington, California. Specimens of Antigorite, Picrolite 2, and Antigorite 99, were from Flagstaff Hill Table 1 Strongest combination bands and OH stretching bands for four different serpentine minerals, given in wave numbers, cmy1. Fe content given as FeO Mineral
Mg–OH a
Clinochrysotile 22 b Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 6 Antigorite 99
4316sh 4315sh 4315
a b
4316sh 4315 4316 4315 4312 4318
OH b 4302 4301 4300 4301 4303 4303 4302 4301 4299 4301 4301
4278 4277 4278 4281 4279 4282 4282 4281sh 4276sh 4272sh 4276sh
Band assignments by Hunt and Ashley Ž1979.. Mineral numbers are from previous study ŽPost et al., 1997..
3691 3694 3696 3692 3692 3690 3692 3689 3687 3690 3697
FeO, %
3686 3685 3685 3676 3675 3675 3676 3675
3651 3650 3647 3651 3653 3652 3652 3651 3651 3651 3652
2.35 2.24 2.02 8.34 9.40 5.56 2.53 4.27 1.91 2.19 5.03
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
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west of Pilot Hill, California, near the Source clay CaRip.1, one specimen of antigorite was from Dawson City, Yuckon Territory, Antigorite 6, and one from northeast of Tucson, Arizona, Antigorite 3. Serpentine specimens 3 and 23 are of metamorphic origin, Class B as described by Faust and Fahey Ž 1962. . All of the remaining specimens are of class A origin. 2.2. Experimental The specimens of serpentine were ground by hand to pass a no. 140 sieve, using specimens visibly pure and showing no impurities by X-ray diffraction ŽXRD. scanning, although most serpentines formed in ultrabasic rocks Ž Class A. contain traces of magnetite.
Fig. 1. Near infrared ŽNIR. combination bands of three serpentine minerals, and of a mixture of lizardite and orthochrysotile.
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
Table 2 Serpentine secondary combination bands given in wave numbers, cmy1, for four different minerals. Specimen 42 is approximately one-half orthochrysotile Mineral
Secondary Mg–OH bandsa
Clinochrysotile 22 b Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 6 Antigorite 99
4212
a b
4217 4211
4205 4200 4206
4171 4162 4173 4165
4129 4117 4110 4133
4197 4204 4214
4169 4196 4196 4196 4198
4125 4123 4128 4123
4107 4095 4102 4098 4087 4106 4078 4076 4083 4077
4080 4033 4032 4049 4065 4032 4013 4010 4000
3980 3987 3984 3985 3974 3988 3980 3975 3976 3971
3874 3914 3910 3907 3886 3910 3874 3893 3884 3894
Band assignments described by King and Clark Ž1989.. Mineral numbers are from previous study ŽPost et al., 1999..
Infrared spectra were obtained using a Perkin-Elmer Fourier-Transform Infrared Spectroscopy ŽFTIR 2000. with a DRIFT attachment. Spectra were
Fig. 2. Infrared fundamental OH stretching bands for three serpentine minerals using diffuse reflectance and using neat powder specimens.
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
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Fig. 3. Infrared fundamental OH stretching bands for three serpentine minerals using transmission scans with KBr pellets containing about 5% serpentine.
recorded using varying scans, from 1 to 15 as needed, with 4 cmy1 resolution. Neat powder was used for reflectance scans from 4700 to 3400 cmy1 wave
Table 3 Serpentine mid-infrared Si–O stretching bands and OH libration bands
Clinochrysotile 22 c Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 99 a
Wave nos., cmy1
OH bands
Si–O bands
Inner a
Outer
dMg–OH b
606 606 611 614 616 622 612 622 623 622
643 650
434 433 439 440 440 441 439 441 441 439
1207 1207 1202
1128 1126 1125
1083 1086 1068 1081 1075 1071 1078 1076 1079 1076
1016 1014 1029 990 984 1008 1017 990 990
959 962 958 957 959 965 956 988 972 972
Inner and outer band designations from Farmer Ž1974.. dMg–OH designation from Ptak Ž1970.. c Mineral numbers are from previous study ŽPost et al., 1999.. b
647 649 641 645
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
number. KBr pellets were made, using about 5% serpentine, for transmission scans from 4000 to 200 cmy1. ASTM standard test procedures were used as listed in the data summary. The scanning electron microscope Ž SEM. micrographs were prepared by Dr. Rolf Nuesch at the Swiss Federal Institute of Technology in Zurich. ¨ ¨ 3. Results 3.1. Infrared spectra The strongest combination band spectra for four serpentine minerals are given in Table 1, with examples in Fig. 1. The spectral band near 4300 cmy1 is
Fig. 4. Infrared spectral bands of three serpentine minerals from 500 to 350 cmy1 including the OH libration band near 441 cmy1 wave number. Clinochrysotile 23 is fibrous and 96 is non-fibrous.
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strongest with a doublet present in clinochrysotile and lizardite spectra as reported by King and Clark Ž1989. . Spectrum Ž E. represents about half lizardite and half orthochrysotile. Specimens 95 and 96 are massive non-fibrous clinochrysotile, and serpentine specimens 3 and 23 were formed in metamorphic rocks as Class B serpentines ŽFaust and Fahey, 1962. . Serpentine secondary combination bands ŽTable 2 and Fig. 1. differ for each serpentine mineral. There are also weak spectral bands near 4450 and 4400 cmy1, and near 3560 and 3600 cmy1, in reflectance mode. Comparison of diffuse reflectance spectra of the serpentine OH stretching bands in Fig. 2 and transmission bands in Fig. 3 show the effects of particle orientation. For example, the antigorite band at 3673 cmy1 remains strong by transmission scan Ž Fig. 3. , while the bands at 3697 and 3652 cmy1 are weaker. Serpentines of Class A and Class B geologic origin appear to have the same infrared spectra. Identification of serpentine varieties by infrared absorption was given by Luce Ž1971. , where he showed that serpentine minerals may be differentiated by Si–O band positions and intensities Ž Table 3. , but not, as he indicated, by the weak OH translation bands near 500 cmy1 wave number, or the dMg–OH band near 440 cmy1, because the band near 500 cmy1 is not present in lizardite and non-fibrous clinochrysotile absorption spectra and the infrared spectra from 500 to 350 cmy1 are nearly the same for these two minerals, as shown in Table 3 and Fig. 4. Mixtures of serpentine mineral spectra may not be readily identified. The infrared spectra of serpentine minerals were presented at the Sili conference in Budapest in 1969 by Ptak and Pampuch, and published by Ptak Ž 1970. . Absorption band assignments for a chrysotile spectrum, from 3700 to 400 cmy1 were given. Only the bands at 472 and 419 cmy1 were missed. 3.2. Aggregate material tests Compacted Serpentine 24 has a maximum density and optimum moisture content, 2110 kgrm3 with 7.3% optimum moisture, similar to illite from the Table 4 Compaction characteristics using ASTM Test Method D1557, Atterberg Limits using method D4318, and axisymmetric compression tests for saturated and for dry serpentine Compaction using Serpentine 24 (8 parts clinochrysotile – 2 parts lizardite) dd max 131.7 pcf Ž2410 kgrm3 ., opt. Moist. 7.3% Atterberg Plastic Limits Antigorite 53 25% Serpentine 24 25% Lizardite 55 36% Axisymmetric Compression Saturated Øs 39.58, cs 0.65 kgfrcm2 Dry Øs 328, cs 0.65 kgfrcm2
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
Empire Mine ŽPost et al., 1997. at 2020 kgrm3 with 11.1% optimum moisture. The Atterberg Plastic Limits show that serpentine is hydrophilic with Plastic Limit contents as high as 36% moisture. Lizardite 55 was discolored by
Fig. 5. Electron optical micrographs of non-fibrous Clinochrysotile 95, ŽA. at 20,000= and ŽB. at 40,000=, and Picrolite 2, ŽC. at 5000= and ŽD. at 15,000=.
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
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Fig. 5 Žcontinued..
descending meteoric water. The Plastic Limit of Serpentine 24 is 22% with a Plasticity Index of 3, very close to being non-plastic. The axisymmetric compression test results ŽTable 4. showed a very high internal friction angle Ž Ø. of 328 when dry and 39.58 when saturated. The
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
82
serpentine has an electronegative surface ŽPost et al., 1999. leading to an effective cementation value, c s 0.65 kgfrcm2. The units of kgfrcm2 are used because they are equivalent to the old construction code requirements of tonrft 2. Serpentine minerals readily break down when tested. When compacted, the material passing the no. 200 sieve increased from 2.4% to 8.4%, and the compression test material, originally all passing a no. 4 sieve and retained on a no. 10 sieve, had 9.6% passing a no. 10 sieve when tested dry and 29.3% passing a no. 10 sieve when tested wet. The specimen mold was 1.40 in Ž3.56 cm. i.d.= 3.5 in Ž8.89 cm. height. 3.3. Electron optical micrographs A specimen of non-fibrous Clinochrysotile 95 was broken across the bedding and electron optical micrographs were made with an SEM in magnification between 500 = and 40,000 = . Micrographs at 20,000 = and 40,000 = are given in Fig. 5 showing the entire specimen consisting of close-packed tubules ˚ diameter, about three times the diameter of fibrous from 600 to 700 A clinochrysotile particles. A specimen of Picrolite 2 was broken along the lath surface and micrographs were obtained at magnifications between 500 = and 15,000 = . Micrographs at 5000 = and 15,000 = are given in Fig. 5.
4. Discussion There is a close relationship between certain absorption bands of serpentine spectra, as shown in Table 5. The first five libration wave number spectral bands Table 5 The relationship between the serpentine combination IR absorption bands, OH fundamental stretching bands, and the lower wave number bands are listed with a comparison of observed and calculated bands for Antigorite 99 Combination y1
Band, cm 4301 4198 4123 4077 4000 3971 3894
s inner s outer s s s s s s
Fundamental
Lower wave no. y1
OH band, cm
Observed, cmy1
Calculated, cmy1
3673 3652 3696 3673 3652 3696 3673 3673
q622 q645 q504 q451 q430 q303 q301 q217
628 649 502 450 431 304 298 221
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
83
have been given OH assignments, and it appears that the remaining four libration spectral bands also should have OH assignments. These band frequency relationships were determined by trial and error summations. The 3673 q 622 cmy1 band frequency relationship was given by Hunt and Ashley Ž1979. and King and Clark Ž1989. . Uehara and Shirozu Ž 1985. believe that the OH band frequency assignments should have the 3696 cmy1 band ascribed to inner hydroxyls and the main 3673 cmy1 band to outer hydroxyls. The NIR spectra for Antigorite 99, listed in Table 6, have the three proposed OH spectral bands marked. Serpentine minerals may be identified by the secondary combination bands and by Si–O infrared band positions and intensities, but mixtures of serpentine minerals may only be identified by XRD methods or optical petroscopy. Lower-temperature serpentines, including clinochrysotile and lizardite, have different physical properties from the higher temperature of formation antigorites. The lower-temperature serpentines have multiple curvilinear parting surfaces and low durability, where massive antigorite has high durability and makes good crushed aggregate material. Both compacted serpentines make good roadway fill. Crushed serpentine passing a no. 40 sieve may be listed as non-plastic when performing the Atterberg Limits ASTM Test Method because threads of moist serpentine may not be rolled to 1r8 in diameter. A better definition of plasticity would be useful. The hydrophilic properties of serpentine are also apparent in the compression test results with the saturated serpentine having a higher internal friction ŽØ.
Table 6 Serpentine far-infrared bands for Antigorite 99, lizardite and clinochrysotile have additional weak bands at 352 and 341 cmy1 wave numbers 400–300 cmy1
300–200 cmy1
400m 385w 372w sh 368w sh 357w sh 328w 319mw 310w 303msa 301mw a
289w 280w 274w 268mw 256mw 252w 241mw 235m 230w 225w 221m 217s a 209m
a
Proposed OH spectral bands. Abbreviations: m — moderate, w — weak, s — strong, sh — shoulder.
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
value than the dry serpentine, and also the cementation Žc. values. Serpentine surfaces have an electronegative charge and hold some cations, as shown by differential thermal analysis scans Ž Post et al., 1999. . The non-fibrous clinochrysotile tubule structure does not appear to be asbestoform because the projecting tubules generally are less than 5 mm long with a low aspect ratio, and the picrolite fibers tend to be too large, and brittle, to be asbestiform ŽCossette, 1982..
5. Conclusions Ž1. Serpentine minerals may be identified by NIR spectral bands, and by Si–O spectral bands. Ž2. Serpentines may not be positively identified by infrared spectra in the ranges of 700–500 cmy1, or the 500–350 cmy1, because the lizardite and non-fibrous clinochrysotile infrared spectra are very similar. Ž3. The infrared spectral bands for antigorite at 431 cmy1, 304 cmy1 , 298 cmy1, and 221 cmy1 probably should be given OH band assignments. Ž4. Serpentine particle orientation is effected when using the KBr pellet method for transmission with some bands such as for the fibrous clinochrysotile 433 cmy1 band Žsee Fig. 4. becoming stronger and other bands not showing. Ž5. Compacted serpentine aggregate material is good for construction fill and crushed antigorite makes good road surfacing. Ž6. Non-fibrous clinochrysotile and picrolite are not asbestiform materials.
Acknowledgements The authors are grateful to Dr. Rolf Nuesch, Institute fur ¨ ¨ Geotechnik — IGT, Zurich, for the SEM microphotos of serpentine minerals. ¨
References Cossette, M., 1982. Defining asbestos particulates for monitoring purposes. In: Levadie, B. ŽEd.., Definitions for Asbestos and Other Health-Related Silicates. ASTM Special Tech. Publ. 834, 213 pp. Farmer, V.C., 1974. The layer silicates. In: V.C. Farmer ŽEd.., The Infrared Spectra of Minerals. Mineralogical Society Monograph 4, 538 pp. Faust, G.T., Fahey, J.J., 1962. The serpentine-group minerals. Geol. Sur. Prof. Paper 384-A, 92 pp. Hunt, G.R., 1977. Spectral signatures of particulate minerals in the visible and near infrared. Geophysics 42, 501–513.
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Hunt, G.R., Ashley, R.P., 1979. Spectra of altered rocks in the visible and near infrared. Economic Geology 74, 1613–1629. Hunt, G.R., Salisbury, J.W., Lenhoff, C.J., 1973. Visible and near infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology 4, 85–106. King, T.V.V., Clark, R.N., 1989. Spectral characteristics of chlorites and Mg-serpentines using high-resolution reflectance spectroscopy. J. Geophys. Res. 24 ŽB10., 13997–14008. Luce, R.W., 1971. Identification of serpentine varieties by infrared absorption. Geol. Sur. Prof. Paper 750-B, pp. 199–201. Post, J.L., Cupp, B.L., Madsen, F.T., 1997. Beidellite and associated clays from the DeLamar mine and Florida mountain area, Idaho. Clays and Clay Minerals 45, 240–250. Post, J.L., Giese, R.F., Madsen, F.T., 1999. Quantitative determination and chemical composition of mineral components comprising serpentine deposits in California in relation to fibrous morphology. Proc. 11th Int. Clay Conf., Ottawa Žin process.. Ptak, W., 1970. Interpretation of chrysotile infrared spectrum. Polska. Akad. Nauk, Oddzial Krakowie, Pr. Kom. Ceram., Ceram. 14, 37–42. Uehara, S., Shirozu, H., 1985. Variations in chemical composition and structural properties of antigorites. Mineral. J. 12, 299–318.
High-resolution infrared spectra, physical properties, and micromorphology of serpentines J.L. Post
a,)
, L. Borer
b
a
b
California State UniÕersity, Sacramento, CA, USA Department of Chemistry, California State UniÕersity, Sacramento, CA, USA
Abstract Separate serpentine minerals may be identified by near infrared ŽNIR. spectra using remote sensing or portable field devices, and identified in the laboratory by NIR and mid-infrared spectra, but X-ray diffraction ŽXRD. procedures are necessary for rapid identification of serpentine mineral mixtures. Compacted serpentine aggregate material is very stable with a density of about 2400 kgrm3 having an internal friction angle of about 328 with weak cementation. Non-fibrous clinochrysotile, the most common serpentine mineral in California deposits, consists of densely ˚ diameter, which are too short to be considered asbestiform. The packed tubules from 600 to 700 A Picrolite fibers are brittle and too large to be asbestiform. q 2000 Elsevier Science B.V. All rights reserved. Keywords: serpentine; clinochrysotile; lizardite; picrolite; fibrous minerals; IR spectra; X-ray diffraction
1. Introduction The California State mineral is serpentine, commonly found in most northern California counties and widely used as crushed aggregate material for construction purposes. Of the numerous small chrysotile asbestos mines, only one remains in operation. The purpose of this study is to show methods of identification of distinct serpentine minerals by infrared spectra involving remote sensing and laboratory testing methods, the results of standard physical tests for construction, and to show the micromorphology of the dominant non-fibrous clinochrysotile serpentine and of picrolite. )
Corresponding author. Vector Engineering, Grass Valley, CA, USA. Tel.: q1-530-478-0542; Fax: q1-530-272-8533 0169-1317r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 1 3 1 7 Ž 9 9 . 0 0 0 4 7 - 2
74
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
The combination spectral bands, with overtone bands of serpentine were given by Hunt et al. Ž1973. and the dominant combination band assignments by Hunt Ž1977. and Hunt and Ashley Ž1979. . This was followed by high-resolution reflectance studies of chlorites and serpentines by King and Clark Ž1989.. The main purpose of these studies was for remote sensing and land surface mapping. Serpentine mineral identification, with chemical analyses, of samples from California was given by Post et al. Ž1999.. Nearly pure specimens of antigorite, clinochrysotile, and lizardite, from a collection of more than 100 analyzed specimens, were chosen for preparing infrared spectra.
2. Materials and methods 2.1. Materials Two specimens of lizardite were obtained, one from a road cut north of Shingle Springs, California, Lizardite 11, and the other from a road cut east of Georgetown, California, Lizardite 51. Specimens of fibrous clinochrysotile were from south of Lake Berryessa, California, Clinochrysotile 22, and from south of Dawson City, Yukon Territory, Clinochrysotile 23, and two specimens of non-fibrous clinochrysotile were from a roadcut on State Hwy 3 north of Weaverville, California, Clinochrysotiles 95 and 96. The Lizardite–Orthochrysotile specimen 42 was from a roadcut northwest of Washington, California. Specimens of Antigorite, Picrolite 2, and Antigorite 99, were from Flagstaff Hill Table 1 Strongest combination bands and OH stretching bands for four different serpentine minerals, given in wave numbers, cmy1. Fe content given as FeO Mineral
Mg–OH a
Clinochrysotile 22 b Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 6 Antigorite 99
4316sh 4315sh 4315
a b
4316sh 4315 4316 4315 4312 4318
OH b 4302 4301 4300 4301 4303 4303 4302 4301 4299 4301 4301
4278 4277 4278 4281 4279 4282 4282 4281sh 4276sh 4272sh 4276sh
Band assignments by Hunt and Ashley Ž1979.. Mineral numbers are from previous study ŽPost et al., 1997..
3691 3694 3696 3692 3692 3690 3692 3689 3687 3690 3697
FeO, %
3686 3685 3685 3676 3675 3675 3676 3675
3651 3650 3647 3651 3653 3652 3652 3651 3651 3651 3652
2.35 2.24 2.02 8.34 9.40 5.56 2.53 4.27 1.91 2.19 5.03
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
75
west of Pilot Hill, California, near the Source clay CaRip.1, one specimen of antigorite was from Dawson City, Yuckon Territory, Antigorite 6, and one from northeast of Tucson, Arizona, Antigorite 3. Serpentine specimens 3 and 23 are of metamorphic origin, Class B as described by Faust and Fahey Ž 1962. . All of the remaining specimens are of class A origin. 2.2. Experimental The specimens of serpentine were ground by hand to pass a no. 140 sieve, using specimens visibly pure and showing no impurities by X-ray diffraction ŽXRD. scanning, although most serpentines formed in ultrabasic rocks Ž Class A. contain traces of magnetite.
Fig. 1. Near infrared ŽNIR. combination bands of three serpentine minerals, and of a mixture of lizardite and orthochrysotile.
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J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
Table 2 Serpentine secondary combination bands given in wave numbers, cmy1, for four different minerals. Specimen 42 is approximately one-half orthochrysotile Mineral
Secondary Mg–OH bandsa
Clinochrysotile 22 b Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 6 Antigorite 99
4212
a b
4217 4211
4205 4200 4206
4171 4162 4173 4165
4129 4117 4110 4133
4197 4204 4214
4169 4196 4196 4196 4198
4125 4123 4128 4123
4107 4095 4102 4098 4087 4106 4078 4076 4083 4077
4080 4033 4032 4049 4065 4032 4013 4010 4000
3980 3987 3984 3985 3974 3988 3980 3975 3976 3971
3874 3914 3910 3907 3886 3910 3874 3893 3884 3894
Band assignments described by King and Clark Ž1989.. Mineral numbers are from previous study ŽPost et al., 1999..
Infrared spectra were obtained using a Perkin-Elmer Fourier-Transform Infrared Spectroscopy ŽFTIR 2000. with a DRIFT attachment. Spectra were
Fig. 2. Infrared fundamental OH stretching bands for three serpentine minerals using diffuse reflectance and using neat powder specimens.
J.L. Post, L. Borerr Applied Clay Science 16 (2000) 73–85
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Fig. 3. Infrared fundamental OH stretching bands for three serpentine minerals using transmission scans with KBr pellets containing about 5% serpentine.
recorded using varying scans, from 1 to 15 as needed, with 4 cmy1 resolution. Neat powder was used for reflectance scans from 4700 to 3400 cmy1 wave
Table 3 Serpentine mid-infrared Si–O stretching bands and OH libration bands
Clinochrysotile 22 c Clinochrysotile 23 Clinochrysotile 95 Clinochrysotile 96 Lizardite 11 Lizardite 51 Lizardite–Orthochrysotile 42 Picrolite 2 Antigorite 3 Antigorite 99 a
Wave nos., cmy1
OH bands
Si–O bands
Inner a
Outer
dMg–OH b
606 606 611 614 616 622 612 622 623 622
643 650
434 433 439 440 440 441 439 441 441 439
1207 1207 1202
1128 1126 1125
1083 1086 1068 1081 1075 1071 1078 1076 1079 1076
1016 1014 1029 990 984 1008 1017 990 990
959 962 958 957 959 965 956 988 972 972
Inner and outer band designations from Farmer Ž1974.. dMg–OH designation from Ptak Ž1970.. c Mineral numbers are from previous study ŽPost et al., 1999.. b
647 649 641 645
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number. KBr pellets were made, using about 5% serpentine, for transmission scans from 4000 to 200 cmy1. ASTM standard test procedures were used as listed in the data summary. The scanning electron microscope Ž SEM. micrographs were prepared by Dr. Rolf Nuesch at the Swiss Federal Institute of Technology in Zurich. ¨ ¨ 3. Results 3.1. Infrared spectra The strongest combination band spectra for four serpentine minerals are given in Table 1, with examples in Fig. 1. The spectral band near 4300 cmy1 is
Fig. 4. Infrared spectral bands of three serpentine minerals from 500 to 350 cmy1 including the OH libration band near 441 cmy1 wave number. Clinochrysotile 23 is fibrous and 96 is non-fibrous.
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strongest with a doublet present in clinochrysotile and lizardite spectra as reported by King and Clark Ž1989. . Spectrum Ž E. represents about half lizardite and half orthochrysotile. Specimens 95 and 96 are massive non-fibrous clinochrysotile, and serpentine specimens 3 and 23 were formed in metamorphic rocks as Class B serpentines ŽFaust and Fahey, 1962. . Serpentine secondary combination bands ŽTable 2 and Fig. 1. differ for each serpentine mineral. There are also weak spectral bands near 4450 and 4400 cmy1, and near 3560 and 3600 cmy1, in reflectance mode. Comparison of diffuse reflectance spectra of the serpentine OH stretching bands in Fig. 2 and transmission bands in Fig. 3 show the effects of particle orientation. For example, the antigorite band at 3673 cmy1 remains strong by transmission scan Ž Fig. 3. , while the bands at 3697 and 3652 cmy1 are weaker. Serpentines of Class A and Class B geologic origin appear to have the same infrared spectra. Identification of serpentine varieties by infrared absorption was given by Luce Ž1971. , where he showed that serpentine minerals may be differentiated by Si–O band positions and intensities Ž Table 3. , but not, as he indicated, by the weak OH translation bands near 500 cmy1 wave number, or the dMg–OH band near 440 cmy1, because the band near 500 cmy1 is not present in lizardite and non-fibrous clinochrysotile absorption spectra and the infrared spectra from 500 to 350 cmy1 are nearly the same for these two minerals, as shown in Table 3 and Fig. 4. Mixtures of serpentine mineral spectra may not be readily identified. The infrared spectra of serpentine minerals were presented at the Sili conference in Budapest in 1969 by Ptak and Pampuch, and published by Ptak Ž 1970. . Absorption band assignments for a chrysotile spectrum, from 3700 to 400 cmy1 were given. Only the bands at 472 and 419 cmy1 were missed. 3.2. Aggregate material tests Compacted Serpentine 24 has a maximum density and optimum moisture content, 2110 kgrm3 with 7.3% optimum moisture, similar to illite from the Table 4 Compaction characteristics using ASTM Test Method D1557, Atterberg Limits using method D4318, and axisymmetric compression tests for saturated and for dry serpentine Compaction using Serpentine 24 (8 parts clinochrysotile – 2 parts lizardite) dd max 131.7 pcf Ž2410 kgrm3 ., opt. Moist. 7.3% Atterberg Plastic Limits Antigorite 53 25% Serpentine 24 25% Lizardite 55 36% Axisymmetric Compression Saturated Øs 39.58, cs 0.65 kgfrcm2 Dry Øs 328, cs 0.65 kgfrcm2
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Empire Mine ŽPost et al., 1997. at 2020 kgrm3 with 11.1% optimum moisture. The Atterberg Plastic Limits show that serpentine is hydrophilic with Plastic Limit contents as high as 36% moisture. Lizardite 55 was discolored by
Fig. 5. Electron optical micrographs of non-fibrous Clinochrysotile 95, ŽA. at 20,000= and ŽB. at 40,000=, and Picrolite 2, ŽC. at 5000= and ŽD. at 15,000=.
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Fig. 5 Žcontinued..
descending meteoric water. The Plastic Limit of Serpentine 24 is 22% with a Plasticity Index of 3, very close to being non-plastic. The axisymmetric compression test results ŽTable 4. showed a very high internal friction angle Ž Ø. of 328 when dry and 39.58 when saturated. The
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serpentine has an electronegative surface ŽPost et al., 1999. leading to an effective cementation value, c s 0.65 kgfrcm2. The units of kgfrcm2 are used because they are equivalent to the old construction code requirements of tonrft 2. Serpentine minerals readily break down when tested. When compacted, the material passing the no. 200 sieve increased from 2.4% to 8.4%, and the compression test material, originally all passing a no. 4 sieve and retained on a no. 10 sieve, had 9.6% passing a no. 10 sieve when tested dry and 29.3% passing a no. 10 sieve when tested wet. The specimen mold was 1.40 in Ž3.56 cm. i.d.= 3.5 in Ž8.89 cm. height. 3.3. Electron optical micrographs A specimen of non-fibrous Clinochrysotile 95 was broken across the bedding and electron optical micrographs were made with an SEM in magnification between 500 = and 40,000 = . Micrographs at 20,000 = and 40,000 = are given in Fig. 5 showing the entire specimen consisting of close-packed tubules ˚ diameter, about three times the diameter of fibrous from 600 to 700 A clinochrysotile particles. A specimen of Picrolite 2 was broken along the lath surface and micrographs were obtained at magnifications between 500 = and 15,000 = . Micrographs at 5000 = and 15,000 = are given in Fig. 5.
4. Discussion There is a close relationship between certain absorption bands of serpentine spectra, as shown in Table 5. The first five libration wave number spectral bands Table 5 The relationship between the serpentine combination IR absorption bands, OH fundamental stretching bands, and the lower wave number bands are listed with a comparison of observed and calculated bands for Antigorite 99 Combination y1
Band, cm 4301 4198 4123 4077 4000 3971 3894
s inner s outer s s s s s s
Fundamental
Lower wave no. y1
OH band, cm
Observed, cmy1
Calculated, cmy1
3673 3652 3696 3673 3652 3696 3673 3673
q622 q645 q504 q451 q430 q303 q301 q217
628 649 502 450 431 304 298 221
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have been given OH assignments, and it appears that the remaining four libration spectral bands also should have OH assignments. These band frequency relationships were determined by trial and error summations. The 3673 q 622 cmy1 band frequency relationship was given by Hunt and Ashley Ž1979. and King and Clark Ž1989. . Uehara and Shirozu Ž 1985. believe that the OH band frequency assignments should have the 3696 cmy1 band ascribed to inner hydroxyls and the main 3673 cmy1 band to outer hydroxyls. The NIR spectra for Antigorite 99, listed in Table 6, have the three proposed OH spectral bands marked. Serpentine minerals may be identified by the secondary combination bands and by Si–O infrared band positions and intensities, but mixtures of serpentine minerals may only be identified by XRD methods or optical petroscopy. Lower-temperature serpentines, including clinochrysotile and lizardite, have different physical properties from the higher temperature of formation antigorites. The lower-temperature serpentines have multiple curvilinear parting surfaces and low durability, where massive antigorite has high durability and makes good crushed aggregate material. Both compacted serpentines make good roadway fill. Crushed serpentine passing a no. 40 sieve may be listed as non-plastic when performing the Atterberg Limits ASTM Test Method because threads of moist serpentine may not be rolled to 1r8 in diameter. A better definition of plasticity would be useful. The hydrophilic properties of serpentine are also apparent in the compression test results with the saturated serpentine having a higher internal friction ŽØ.
Table 6 Serpentine far-infrared bands for Antigorite 99, lizardite and clinochrysotile have additional weak bands at 352 and 341 cmy1 wave numbers 400–300 cmy1
300–200 cmy1
400m 385w 372w sh 368w sh 357w sh 328w 319mw 310w 303msa 301mw a
289w 280w 274w 268mw 256mw 252w 241mw 235m 230w 225w 221m 217s a 209m
a
Proposed OH spectral bands. Abbreviations: m — moderate, w — weak, s — strong, sh — shoulder.
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value than the dry serpentine, and also the cementation Žc. values. Serpentine surfaces have an electronegative charge and hold some cations, as shown by differential thermal analysis scans Ž Post et al., 1999. . The non-fibrous clinochrysotile tubule structure does not appear to be asbestoform because the projecting tubules generally are less than 5 mm long with a low aspect ratio, and the picrolite fibers tend to be too large, and brittle, to be asbestiform ŽCossette, 1982..
5. Conclusions Ž1. Serpentine minerals may be identified by NIR spectral bands, and by Si–O spectral bands. Ž2. Serpentines may not be positively identified by infrared spectra in the ranges of 700–500 cmy1, or the 500–350 cmy1, because the lizardite and non-fibrous clinochrysotile infrared spectra are very similar. Ž3. The infrared spectral bands for antigorite at 431 cmy1, 304 cmy1 , 298 cmy1, and 221 cmy1 probably should be given OH band assignments. Ž4. Serpentine particle orientation is effected when using the KBr pellet method for transmission with some bands such as for the fibrous clinochrysotile 433 cmy1 band Žsee Fig. 4. becoming stronger and other bands not showing. Ž5. Compacted serpentine aggregate material is good for construction fill and crushed antigorite makes good road surfacing. Ž6. Non-fibrous clinochrysotile and picrolite are not asbestiform materials.
Acknowledgements The authors are grateful to Dr. Rolf Nuesch, Institute fur ¨ ¨ Geotechnik — IGT, Zurich, for the SEM microphotos of serpentine minerals. ¨
References Cossette, M., 1982. Defining asbestos particulates for monitoring purposes. In: Levadie, B. ŽEd.., Definitions for Asbestos and Other Health-Related Silicates. ASTM Special Tech. Publ. 834, 213 pp. Farmer, V.C., 1974. The layer silicates. In: V.C. Farmer ŽEd.., The Infrared Spectra of Minerals. Mineralogical Society Monograph 4, 538 pp. Faust, G.T., Fahey, J.J., 1962. The serpentine-group minerals. Geol. Sur. Prof. Paper 384-A, 92 pp. Hunt, G.R., 1977. Spectral signatures of particulate minerals in the visible and near infrared. Geophysics 42, 501–513.
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Hunt, G.R., Ashley, R.P., 1979. Spectra of altered rocks in the visible and near infrared. Economic Geology 74, 1613–1629. Hunt, G.R., Salisbury, J.W., Lenhoff, C.J., 1973. Visible and near infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology 4, 85–106. King, T.V.V., Clark, R.N., 1989. Spectral characteristics of chlorites and Mg-serpentines using high-resolution reflectance spectroscopy. J. Geophys. Res. 24 ŽB10., 13997–14008. Luce, R.W., 1971. Identification of serpentine varieties by infrared absorption. Geol. Sur. Prof. Paper 750-B, pp. 199–201. Post, J.L., Cupp, B.L., Madsen, F.T., 1997. Beidellite and associated clays from the DeLamar mine and Florida mountain area, Idaho. Clays and Clay Minerals 45, 240–250. Post, J.L., Giese, R.F., Madsen, F.T., 1999. Quantitative determination and chemical composition of mineral components comprising serpentine deposits in California in relation to fibrous morphology. Proc. 11th Int. Clay Conf., Ottawa Žin process.. Ptak, W., 1970. Interpretation of chrysotile infrared spectrum. Polska. Akad. Nauk, Oddzial Krakowie, Pr. Kom. Ceram., Ceram. 14, 37–42. Uehara, S., Shirozu, H., 1985. Variations in chemical composition and structural properties of antigorites. Mineral. J. 12, 299–318.