Clay Minerals (1984) 19, 789-801

T H E R M A L A N A L Y S I S IN THE I N V E S T I G A T I O N OF Z E O L I T I Z E D A N D A L T E R E D V O L C A N I C S OF

L A T I U M , I T A L Y

G. L O M B A R D I

Istituto di Mineralogia e Petrografia, Universitd degli Studi di Roma 'La Sapienza', Cittd Universitaria, 00185 Roma, Italy

(Received 3 February 1984)

A B S T R A C T : The data obtained on zeolites, kaolins, alunites, hydrated sulphates and soils by DTA-TG-EGA carried out under various experimental conditions are discussed. Among the main subjects dealt with are chabazite and phiflipsite identification and their quantification by TG, clay mineral distribution in size fractions of kaolins, significance and use of thermoanalytical data from alunitic rocks, the influence of calcite and calcined kaolinite on the sulphate DTA curves, rates of decomposition of hydrated sulphates, and thermal analysis of soils in forensic studies.

To the north-west of Rome, the region of Latium (Fig. 1) is characterized (Locardi et al.,

19 77) by extensive volcanic outcrops related to the activity of: (i) The Upper Pliocene-Pleistocene acidic groups of Tolfa-Ceri t i -Manziate (average

age 2.5 Ma) and of Mt. Cimino (1 .4 -1 .0 Ma), where rhyolites and quartz-latites, lavas and ignimbrites, dominate.

(ii) The more extensive alkaline-potassic groups of Vulsini, Vico and Sabatini (ages between 0.9 and 0.01 Ma) where pyroclastic flows, tufts and subordinate lavas have compositions varying from tephritic-latitic-trachytic to leucititie.

A major thermal anomaly is the main source of the energy which contributed to the large scale fluid circulation responsible for considerable alteration and mineralization processes. Final products are very varied as they result from interactions between fluids with a broad range of temperatures and chemical compositions, and host rocks of widely different lithologies (Lombardi & Mattias, 1979).

This paper discusses recent D T A - T G - E G A data obtained under various experimental conditions on zeolites, kaolins, alunites, hydrated sulphates and soils derived from both the acidic and alkaline-potassic volcanics of Latium.

Z E O L I T E S

The characteristics of the pyroclastic flows of the alkaline-potassic volcanic groups of Latium are very variable, depending on emplacement mechanisms, cooling modes, fluid-silicate reactions and diagenesis. There are compact, mechanically-resistant facies which can be cut into thin slabs, porous facies with densities of 1.40 g/cm 3 which are utilized as building blocks, and incoherent pozzolana-type materials used for mortar

�9 1984 The Mineralogical Society

790 G. L o m b a r d i

l ~ Bolsena'""" "}l ~ l l ~ ~ Lake Umbric

! " " ~ : .:- . - . . . . . . . . .

" ~ :'i':" .': .i L.: ~Vl tAerbo

"."; : : : Mr. Cirnino (

i ~. )!?"::::" vJoo ,. _.o

. . . . . . . . . ,o,P" T O L F A . ' " . . ! : " ' "~ . . . . . . ' " " "

( - ~ . "" Brocclono

Civitove~chio M A N Z I A T E . ~ t E ~ t \~ . ~ ' ~ \ CERIT I .:" ~ r

TYRRHENIAN

SEA

"'.....

:....:

Rome

0 I0 20 30 K m

FIG. 1. Map of north west Latium with approximate boundaries of the alkaline-potassic volcanic groups of Vulsini, Vico and Sabatini, and of the acidic groups Tolfa, Ceriti and Manziate.

preparation. These variations are often related to the influence of argillization and zeolitization processes. As a result of diagenetic reactions in regions close to the water table, halloysite became abundant; such facies tend to be incoherent. When alkaline conditions prevailed, during cooling or in later diagenesis, zeolites (mainly chabazite, phillipsite and analcite) developed and these may form a substantial portion of the total rock, which becomes lithic.

Identification and quantification of the zeolites are important for genetic studies, planning of building-block quarries and assessment of the commercial value of pyroclastic facies as potential sources of industrial zeolites.

For the work described in this section, analyses were carried out on zeolitized pumices (diameter from a few mm to several cm) sampled from a 50-m high face of a quarry in the 'Tufo Giallo della Via Tiberina' pyroclastic flow, 15 km north of Rome (Nappi et al., 1979; Bianchetti et al., 1982). These pumices provided a relatively homogeneous glassy 'parent-rock' and an assemblage of only zeolites and glass. By sampling one formation and related quarry, the variability connected with different magma types, mode of emplace- ment, age and length of diagenesis was greatly reduced.

Chabazite and phillipsite may occur together and DTA curves provide a means of assessing their ratio. Fig. 2a shows a sequence of samples from the lower phillipsite-rich levels to the upper part of the quarry, where chabazite is dominant. Though water losses appear to be continuous when analysed dynamically, they are well discriminated by DTG (Fig. 2b), which allows quantitative estimations of the different types of released water.

XRD offers a potentially easy means of identification for the various zeolites present, but the glass -, partially zeolitized glass --, zeolites transition and differences in crystallinity

Thermal analysis of altered voleanies 791

Zeolitized pumices

117

AC C68 ~ r 16~

C 10 y

K-chabazite From pumice

100 300 "C

Zeolitized pumice

100 200 300 ~ Fro. 2. (Left) DTA curves of phillipsite crystals from a geode, of five untreated samples of pumices with various phillipsite and chabazite contents and of a K-chabazite separated from a pumice. Total weight losses at 350~ are shown on the right of each curve. (Right) DTA, TG and DTG of a chabazitic pumice (sample C of Fig. 3). DTG (and DTA) indicate a two-step weight loss which is not evident from TG only. Heating rate 10~ N 2 flow; sample weight

5 mg; reference: A!203. Stanton Red croft equipment.

make actual quantification in these formations difficult. D T A curves and formalized X R D patterns of four chabazitic samples from a single block of zeolitized pyroclastic flow are shown in Fig. 3. The B - A - C - E order is based on the chabazite DTA peak size and connected weight loss; it does not correspond well to the relative heights of the peaks on the X R D patterns, although the positions of the various chabazite peaks coincide.

A method recently developed at the University of Naples (Colella et al., 1983) provides a reliable and rapid quantification of phillipsite and chabazite in volcanic rocks. It is based on TG and the fact that water readsorption properties of phillipsite and chabazite are not affected by heating to 240 ~ and 350~ respectively.

As illustrated in Fig. 4, the water of the glass (irreversible reaction) is released by heating isothermally at 240~ to constant weight. The total readsorption of water by the phillipsite is then obtained by cooling and introduction of H20 vapour. Further heating to 350~ causes the collapse of the phillipsite structure and the reversible loss of the chabazitic water, which can be estimated by raising the temperature to 800~

792 G. L o m b a r d i

Chabaz i t i c pumices

, . , . , Jl,I

I I , ' \ #5 It

1.1,, , I . i l I,

, , , , . . . 1 ! . , . �9 I I . 100 200 300 ~ 2 theta 3'0

,I, l f l l , . , I . , I .. ] • B

It, i l l . . . . I

~ E 20 10

FIG. 3. DTA curves (experimental conditions as in Fig. 2) and XRD patterns (Ni-filtered Cu-Ka radiation; scanning speed 1 o 20/min) of four chabazitic pumices. Samples from one single block

(approximately 40 • 25 • 15 cm) of the 'Tufo Giallo della Via Tiberina' pyroclastic flow.

Zeolitized 'tuff' ~ 3% loss in TG

TG'~Glass water -? - f ~ " ~ - Phillipsite ~ ~ ~ . water k__

I ~ k - ~q-~__C_habazite~water Introduction ~ - - - ~

H20~ H20 vapor 800~/k. .__ il~ ~1 I1~ '411

o , - - -~ I~ 350 ~ / ' \ / 25 ~ ~ 25 ~c \ ~ 25 ~

FIG. 4. A scheme for the determination by TG of the chabazite and phillipsite contents in zeolitized pyroclastic material. Based on data in Colella et al. (1983) and d6 Gennaro et al.

(1983).

The glass-water and the phillipsite and chabaz i te contents can be quantif ied by this

m e t h o d with results which are in ve ry good agreement with those der ived f rom more

c u m b e r s o m e techniques , such as ion-exchange capac i ty m e a s u r e m e n t s (Colel la et al.,

1983).

Thermal analysis of altered voleanies 793

K A O L I N M I N E R A L S

Kaolinite, dickite and halloysite, in decreasing order of abundance, are among the main constituents of the altered acidic lavas and ignimbrites of the Tolfa-Ceriti volcanic groups and are often associated (Lombardi & Mattias, 1979). Halloysite (both 7A and 10A) is the only common kaolin mineral found in the altered alkaline-potassic volcanics.

DTA, XRD and IR data for natural samples with variable kaolinite/dickite ratios and contents were given by Lombardi & Sheppard (1977). DTA can provide a very good assessment of the variation in these ratios, which is more difficult or impossible to assess by X-ray analysis only.

It should be noted that thermoanalytical and X-ray data from whole-rock analyses are averaged from a number of different size fractions which may have very different mineralogical and/or structural characteristics (Keller & Haenni, 1978). In Latium, kaolins originate from a complex sequence of events and interactions which superimposed different records on a very small scale. Therefore, in a single hand-specimen mineralogical imprints of different environments and stages are often preserved.

A study of a kaolin sample from Latium (Lombardi et al., in preparation) illustrates the contribution which D T A - T G can offer to identification and quantification of clay mineral associations in different size fractions. Dickite was found in the coarser fractions and kaolinite with progressively lower crystallinity, mixed-layer illite-montmorillonite and illite in the finer fractions, where TEM and SEM images often showed the presence of halloysite and allophane.

Quantitative data can be obtained from TG weight losses; they are very reliable as they are independent of the degree of crystallinity of the clay minerals, which strongly influences peak morphology, size and temperatures on the DTA curve and the resolution of XRD patterns.

However, even fairly large thermal effects of halloysite (and allophane) can go undetected in those facies where kaolinite and dickite plus mixed-layer illite- montmorillonite and illite dominate. Moreover, Keller & Haenni (1978) showed that in artificial mixtures of kaolin polymorphs the presence of even 25% of one end-member can be masked by the dominant type. Therefore, great care must be taken in the interpretation of data from these natural mixtures, and use of more than one analytical technique is essential to substantiate results.

A L U N I T E S

Minerals of the alunite series (mainly alunite, KA13(OH)6(SO4) 2, with variable sodium contents) are common accessories in hydrothermally-altered volcanics, but only at a few locations, such as Tolfa-Allumiere, do they become the main components. In this area about 70% of a 40 km 2 volcanic massif shows alteration and mineralization related to both hydrothermal and supergene processes (Field & Lombardi, 1972). More than 18 million tons of alunite were extracted from the area between 1465 and the beginning of this century. The cement industry still uses few thousand tons each year.

The DTA curve of alunite is characterized by three peaks. In conjunction with TG data, these may provide identification of the member of the alunite series (i.e. its approximate Na: K ratio), a fairly accurate estimation of the alunite content, and the nature of the most common impurities associated with the sulphate.

794 G. Lombardi

AJunites

I I I I

I I [ I 500 I000

To ®

DTG DTA

I I I I

D T G

I I I I

.oL

I I I I I I , SOs 500 1000 500 I 0 0 0 "C

FIG. 5. Simultaneous TG-DTA-DTG-MS of three alunitic samples. (A) Tolfa, Latium, >95% alunite with K/Na rato of 1.2. (B) Torniella, Tuscany, >95% alunite with K/Na ratio of 4.5. (C) Mezzano, Latium, ~67% alunite with K/Na ratio of 2.2. Heating rate 10°C/rain; air flow; sample weight 100 rag; reference: A1203; mass spectrometer sensitivities:

m/e (A) (B) (C) 18 [H~O]" 10-gA 10-9A 10 9A 48 [SO] + 10 -7 A 10 -9 A 10 l0 A 64 [SO2] + 10 -7 A 10 -9 A 10 9 auto 80 {SO3] + 10 -11A 10 12A 10-1ZA

From all three alunites various quantities of CO 2 were also evolved. Netzsch equipment. Data for sample C have been published by Kaiserberger (1982).

Fig. 5 displays D T A - T G - D T G - M S curves of alunites. The large dehydroxylation peak at 550°C may mask effects due to associated kaolin minerals and quartz. However, the presence of kaolin minerals can usually be confirmed by the exothermic high-temperature peak and these minerals quantified from any hydroxyl water in excess of that evolved from aluni te-- the latter figure being calculated from measurements of the evolved sulphur species and knowledge of the stoichiometry of the particular alunite. Quartz may be revealed (and quantified) on a D T A cooling curve using the reversible phase transition at ~575°C.

The exothermic peak at 750°C is typical of K-rich alunites and in samples with a K / N a ratio less than 60 :40 it does not develop (Otsuka, 1977). In natural samples (Lombardi & Sonno, 1979) its appearance may be inhibited by the presence of impurities. K / N a ratios can also be calculated from the temperature of the endothermic peak associated with the main loss of sulphur compounds (Otsuka, 1977), with an approximation close to that obtainable from X R D , by using diagrams such as the one proposed by Cunningham & Hall (1976).

The second endothermic peak of alunite may be used for quantitative analysis. Kashkai

Thermal analysis of altered volcanics 795

(1970) presented diagrams relating SO3 to K- and Na-alunite contents. However, the SO 3 loss occurs in several steps on the TG curves and therefore an empirically-determined range must be chosen. For example, Lombardi (1967) reported a good correlation between weight losses in the 700-850~ range from TG curves and chemically-determined alunite contents. Less accurate content estimations may be obtained from measurement of the area of the corresponding DTA peak.

In TG-based calculations it is assumed that SO 3 is released after the end of the H20 emission, marked on the TG curve by a decrease in the rate of weight loss. In fact, EGA analysis shows that the gas evolution sequence is complex and may vary in different samples and under different experimental conditions.

Morgan (1977) presented D T A - E G A curves of alunite which indicated that there was some overlap of the HzO and sulphur-compound emissions, with SO 2 evolving from approx. 570~ Under the vacuum conditions of a simultaneous thermal analysis-mass spectrometer system, Muller-VonMoss (personal communication) found that sulphur compounds began to evolve from alunite at temperatures as low as 400~

Fig. 5 shows the simultaneous D T A - T G - D T G - E G A curves of three alunite samples with different K/Na ratios. EGA was carried out by quadrupole mass spectrometer; the curves for samples A and B (>90% pure alunite) show very similar H~O release patterns and reveal that there is a partial readsorption at ~800~ SO 3 appears to be released in significant quantities even at 550~ in the same range as the main H20 loss, whilst SO 2 and (in samples B and C only) SO losses begin later. In sample C, amorphous silica and halloysite impurities markedly affect the alunite decomposition; H20 loss occurs at higher than usual temperatures and sulphur compounds show different evolution patterns.

Overlap of effects due to different components in a mixture occurs both on thermal

~ ite

10 0

10 5

10 10

I I I 400 800 ~

0 10

10 15

I0 20 ~ ~ _

10 3O " ~ l

400 800 ~

FIG. 6. DTA curves of artificial mixtures with various calcite/alunite ratios. High-temperature solid-state reactions occur between the decomposition products of alunite and calcite. Heating rate 10~ static air; samples diluted with A1203 (also used as reference) to an approximate

weight of 300 mg. Netzsch/Leeds-Northrup equipment.

796 G. Lombardi

curves and X-ray traces. In X-ray work they can be allowed for by checking relative peak intensities and their attribution to different phases. In thermal analysis, cooling curves, addition of one phase to the inert and computer-assisted analysis of peaks are examples of how to deal with overlapping affects. Attention must also be paid to the possibility of high-temperature solid-state reactions between decomposition products. They may lead to extreme modifications of the DTA and TG curves which are potentially disastrous for uncautious investigators.

Several examples of these solid-state reactions may be found in the literature; two instances related to alunites are described below.

Although not common, alunite may be found in carbonate-rich environments (Caillere & Maratos, 1958). Fig. 6 shows DTA curves of alunite-calcite artificial mixtures which indicate that the alunite dehydroxylation peak is only mildly affected by the presence of calcite. However, when simultaneous desulphurization and decarbonation occur, both DTA and TG curves may be far removed from any theoretically predicted pattern.

Reaction between the decomposition products of alunite and calcined kaolinite used as diluent may also occur (Fig. 7). At about 1050~ a well-defined endothermic peak related to K2SO 4 decomposition develops in diluted samples and reaches a maximum at a 5:3 sulphate : calcined kaolinite ratio.

~ K2S04 sandwich of "~ / ~ ~ . ~ J alunite-calc, kaol. alunite-calc kaol

3 5

5 3

7 0

P

I I _ _

200 600 1000 ~

FIG. 7. DTA curves of alunite diluted with various quantities of calcined kaolinite. From their decomposition products, a peak develops at 1050~ From X-ray and TG evidence (not reported), the peak appears to be related to the breakdown of K2SO 4 (redrawn from Lombardi, (1967). Heating rate 10~ static air; sample weight 1.5 g; reference: calcined kaolinite.

Netzsch/Leeds-Northrup equipment.

Thermal analysis of altered volcanies 797

The existence of these high-temperature reactions emphasizes that knowledge of sample mineralogy is essential before attempting any quantitative or, in some cases, qualitative work based on D T A - T G curves.

H Y D R A T E D S U L P H A T E S

In mineralized areas of both the alkaline-potassic and the acidic volcanics, meteoric water interaction with sulphide impregnations leads to the formation of assemblages of hydrated sulphates of iron (mainly) and other cations. Rozenite, FeSO4.4H20, siderotil, FeSO4.5H20, melanterite, FeSOn.7H20, coquimbite, Fe2(SOa)3.9H20, pickeringite, MgA12(SO4)4.22HzO, halotrichite, FeA12(SOa)a.22H20, and chalcantite, CuSO4.5H20, are among the species identified in the Latium region.

Their thermoanalytical curves show two main sets of peaks, one below 350~ and one between 450 ~ and 800~ related to H20 and sulphur compound release, respectively. Heats of reactions tend to be large: this factor, together with the often complex peak system resulting from water loss, means that individual species can be identified at quite low concentrations using DTA.

Fig. 8 gives the DTA curves for two such sulphates. In rozenite, loss of water is represented by a very sharp reaction and, consequently, a very deep peak. Chalcantite loses its larger water content over a wider temperature range and its peaks are contained on the chart under the experimental conditions of these runs.

The unpredictable peak dimensions of these materials provide a good case for computer storage of data from the runs. In addition to other benefits, this markedly increases productivity by saving runs carried out at inadequate sensitivities.

/ Rozenite FeS04.4H20

100 300

15o 350 sso 7so "C-

FIG. 8. DTA curves of rozenite and chalcantite. The very sharp rozenite peak has been schematically redrawn. Experimental conditions as in Fig. 2. Sample weight 6 rag. The insert shows the different peak shapes in the low temperature region oftamarugite given by three runs with loosely-packed samples. Heating rate 10~ static air; sample weight 11.3 rag;

reference: calcined kaolinite. Merrier equipment. (From Lombardi & Sposato, 1981).

798 G. L o m b a r d i

With large amounts of H20 released in diverse, close steps, the degree of compaction and internal structure of the sample within the crucible greatly influences peak characteristics. Even duplicate runs with loosely-packed microsamples may produce different peak heights and dimensions, as shown in the low-temperature region of the tamarugite DTA curves reproduced in the insert of Fig. 8.

V O L C A N I C ' S O I L S '

Although the field of work of the Author is not directly concerned with the study of volcanic soils, his frequent forensic work in col|aboration with Police Forces of Latium has often led to the necessity of characterizing soil materials, such as those found on clothes, shoes and cars.

Criminal events generally occur in built-up areas and samples are therefore composed of:

(i) a mineral fraction with abundant aluminosilicates; (ii) an organic fraction with fragments of plants, shells, insects, seeds and pollen;

(iii) an anthropogenic fraction with plastic, fibre, rubber, metal, ceramics, bricks and glass fragments.

Such samples give unique D T A - T G curves resulting from the sum of the effects of these components, present in variable ratios depending on the genetic histories of the micro-environment. These curves are very useful since--besides identifying the composit ion--i t is often essential to offer objective evidence of sample similarity or non-similarity. Two cases will illustrate such applications.

Running away after killing a jeweller in a hold-up, a criminal left shoemarks on a wet volcanic soil close to the car he abandoned. In a suspect's house, 30 km away from where the car was found, Police confiscated a pair of muddy shoes.

A B C = field / ~ /

J r , =

A A'

B

B'

C' I I I I I I _

100 500 900 ~

FIG. 9. TG (A-A'), DTA (B-B') and DTG (C-C') of soils sampled from a field and from a muddy shoe (from Gualdi et al., 1974). Experimental conditions as in Fig. 8. Sample weight

250 mg.

Thermal analysis of altered volcanies 799

_ _ t L t 1 q I I h [ I

100 ,t00 700 IO00~

FIG. 10. DTA and TG of a dried-up soil fragment (A and B), found in the boot of a car, and of a volcanic soil (A' and B') from a grave. Heating rate 5~ air flow; sample weight as

indicated. Mettler equipment.

Fig. 9 shows the D T A - T G - D T G curves of samples from the shoes and the soft. The curves are complex, with peaks of halloysite (endotherms at I10~ and 520~ and an exotherm at 900~ of vegetals (exotherm at 300~ and of iron hydroxides (endotherm at 340~ but not all the effects can be accurately explained. However, the overall similarity of the patterns of all three sets of curves is close indeed for a multicomponent sample. Together with XRD and other data which confirmed the similarities of the crystalline fraction, these curves helped to prove the participation of the suspect in the hold-up murder.

In another case, a man was kidnapped, killed and his body buried 45 km away from the beach house used as a prison. A car was supposed to have been used to carry the body to the place where it was buried, characterized by soil derived from alkaline-potassic volcanics,

A careful examination of the dirt in the car boot revealed in it ~ 1% of fragments, a few mm in diameter, of brownish earthy material. Although several months had elapsed since the body was recovered, samples from the burial place were collected and compared.

XRD patterns were similar, but were also common to many other volcanic-rock-derived soils of Latium. D T A - T G curves (Fig. 10) were more decisive, these being identical apart from a smaller low-temperature weight loss in the dried-up sample from the car boot.

C O N C L U S I O N S

The results discussed here confirm the high potential value of thermal analysis for the characterization of mineral assemblages from recent volcanics and from their alteration products. In conjunction with XRD, IR and chemistry, thermoanalytical data can help to overcome the problems related to specific aspects of these assemblages, such as variable

800 G. L o m b a r d i

degree of crystal l ini ty, extensive i somorphous subst i tut ions, and marked composi t ional and

s t ructural var ia t ions in the different size fractions. S imul taneous techniques used here are very helpful. D T A provides basic informat ion ,

T G plays a key role in quant i ta t ive assessments and E G A allows de te rmina t ion of the

sequence of the decomposi t ions . The benefits f rom these techniques can be greatly

enhanced by adequate software of a computer-ass is ted ins t rument . F o r example, this helps the in terpre ta t ion of over lapping effects f rom assemblages which are very rarely t ruly monominera l i c , stores data f rom different ou tputs wi thout concern for ins t rumenta l

sensitivities, enables homogeneous data quant if icat ions, and provides sets of graphical ly

adequate curves for reproduct ion. However , the qual i ty of results from studies of mater ia ls derived from recent volcanics

still very much depends on the opera tor ' s experience, which heavi ly influences the level of

in terpre ta t ion of the in format ion obta ined from the exper imental data.

A C K N O W L E D G M E N T S

The Author thanks Professor M. dd Gennaro and E. Franco of the University of Naples for helpful discussions on zeolite quantification, Professor A. La Ginestra of the University of Rome for use of his thermoanalytical equipment and Netzsch and Stanton Redcroft for analyses carried out in their research laboratories.

R E F E R E N C E S

BIANCHETTI P.L, LOMBARDI G. & MEUCCI C. (1982) Study of the degradation of 'tuff' blocks used in the Roman Temple of Cibeles (Rome, Italy). Pp. 29-38 in: Proc. Fourth Int. Cong. on the Deterioration and Preservation of Stone Objects, Louisville, Kentucky, July 7-9, 1982 (K. L. Gauri & J. A. Gwin, editors). The University of Louisville, Kentucky, USA.

CAILLERE S. & MARATOS G. (1958) Sur la pr6sence et l'origine de l'alunite dans les phyllades de l'ile de Crdte (Gr6ce). Bull. Soe. Franc. Mindr. Crist. 81, 16-18.

COLELLA C., Di GENNARO M., FRANCO E. & AIELLO R. (1983) Estimation of zeolite content in Neapolitan Yellow Tuff. I. Phillipsite in nearly mono-zeolitic deposits. Rend. Soc. It. Miner. Petr. 38, 1423-1427.

CUNNINGHAM C.G. • HALL R.B. (1976) Field and laboratory tests for the detection of alunite and determination of atomic percent potassium. Eeon. Geol. 71, 1596-1598.

DE GENNARO M., COLELLA C., FRANCO E. & AIELLO R. (1983) Italian zeolites 1. Mineralogical and technical features of Neapolitan yellow tuff. Ind. Miner. 186, 47-53.

F~ELD C. & LONBARD~ G, (1972) Sulfur isotopic evidence for the supergene origin of alunite deposits, Tolfa district, Italy. Miner. Deposita 7, 113-125.

GUALDI G., LOMBARD1 G., LOPEZ A. & MARRACINO F. (1974) Indagini su campioni di terreno ai fini della identificazione di un autore di reato. Pp. 487-494 in: Seritti in onore di Cesare Gerin 2. Universitfi degli Studi di Roma, Rome.

KAISERBERGER E. (1982) Ceramics--new applications in a traditional field of thermal analysis. J. Thermal Anal. 25, 181-190.

KASHKAI M.A. (1970) Alunites, Their Genesis and Utilization 1, pp. 172-178. NEDRA Publishing House, Moscow.

KELLER W.D. & HAEmq R.P. (1978) Effects of micro-sized mixtures of kaolin minerals on properties of kaolinites. Clays Clay Miner. 26, 384-396.

LOCARDI E., LO~BARDI G., FUNICIELLO R. & PAROTTO M. (1977) The main volcanic groups of Latium (Italy): Relations between structural evolution and petrogenesis. Geol. Romana 16, 279-300.

LOMaAROI G. (1967) Ricerche su rocce alunitiche del settore di Tolfa-Allumiere (Lazio). Periodico Miner. 36, 399-450.

LOMBARDI G. & MATnAS P. (1979) Petrology and mineralogy of the kaolin and alunite mineralizations of Latium (Italy). Geol. Romana 18, 157-214.

Thermal analysis o f altered voleanics 801

LOMBARDI G. & SONNO M. (1979) Studio petrografico dell'alunite di Mezzano e di altre vulcaniti alterate della Caldera di Latera (Vulcani Vulsini, Lazio). Periodico Miner. 48, 21-52.

LOMBAROI G. & SPOSATO A. (1981) Tamarugite from Vulcano, Aeolian Islands, Italy. Can. Miner. 19, 403-407.

MORGAN D.J. (1977) Simultaneous DTA-EGA of minerals and natural mineral mixtures. J. Thermal. Anal. 12, 245-263.

NAPPI G., De CASA G. & VOLPONI E. (1979) Geologia e caratteristiche del Tufo Giallo della Via Tiberina. Boll. Soe. Geol. It. 98, 431-445.

TSUTSUMI S. & OTSUKA R. (1977) Thermal studies of the alunite-natroalunite series, (K,Na)A13(SO4)2(OH) 6. Pp. 456-459 in: ThermalAnalysis (H. Chihara, editor). Kagaku Gijutsu-sha, Tokyo.