D. 8. Inst. Geol. Geofi ,z. vol. .741L (1987), 1989, pag. 181-189

I. iI,TINERALOGIE -PETROLO GIE

P E T ROLOGIA ROCILOR M AG trl AT IGE

YOI,CANIC BOMRS ANI] BLOCKS IN IIARGHITA MTS 1

by

ALtr\ANI)I iU SZAKACST, CSABA JANOSIS

Volcanic rocks. Daciles. Andesites. l'olcanoclastics. |ieogene. East Carpathians - Neogene

eruptiue-Quaternarg - H arghila )Iountains.

Abstract

Morphology and structurc of dacitic and andesitic polygonal volcanic bombs and blocks

from occurnences in trvo areas of Harghita llts (Ciomadul massi{ in South Harghita and west

Dinegti in North Harghita) are described. A great number of bombs and blocks show bread-

crust cracks and chilled margin. Bombs vith radial impact cracks for the first time are poin-

ted out.

R6sum6

Bombes aolcaniques des monls de Harghita. On fait, pour la premidre fois dans notre pays,

une description morphologique et structo-texturale des bombes volcaniques polygonaux i com-

position dacitique et and6sitique localis€es en deux occurrences des monts l{arghita (massif de

Ciomadul et la zone situ6e i I'ouest de la localit6 de Dinegti). Une grande partie des bombes

pr6sente des fissures de type ,,crotte de pain" et un bord vitreux. On signale. en premidre,

la pr6sence cle quelques bombes i fissures radiaires d'impact-

1 Received NXay 11, 1987, accepted for communication and publication May 12, 1987,

presented at the meeting May 22, 1987.2 Institutul de Geologie Si Geofizici. Str. CaransebeE nr. 1, R 79678 Bucuregti, 32.s Intreprinderea de Prospectiuni pi Exploriri Geologice ,,F{arghita". Str. Gh. Doja nr. 6,

R 4100, Miereurea Ciuc, Harghita.

t \2 AI. SZAI{ACS, CS. JANOSI

Introduetion

Bread-cruqt type volcanic bcmbs were for a long time knov'n inCiomadul massif, south-east of South Ilarghita Mts lCho-tnoty, tg2p eiteclby Bdnyai' 1964). There are.some_speeiriens in the Geotogy-ivriner.alogyDepartment's collection withiq Bab6t-Boiyai Ilniversity itr"bt..j-Naporie,originating from this region. They dicl noi subject t" ;hy volcanologic,raistudy until no'w.

Basaltic volcanic'bomhs'wc:re desclibed by Feltz (in Mihili l[ et a].,7972 and Mihdil5,? Peltz, 1977) 'u.ithin I' leistocene volcanic pro4ucts i1Perqani Mts.

In the neogene r,oltanit ; areas in Rcniania, ( ' icrnadul nrassif andPerqani Mts constitute the cnly kno.n,n occurr€nces of volcanic bombs a.

.This-P-aFer proposes to t l tscr" i l ,e dar. i t i r . rolcanjc: bcmbs and blocksIn ( ' lomaclu l massi f anc l ant les j t i t ,ones I ' rcm an unknc$n occtu, rence inNorth }larghita l\Its.

Geologieal Set{ingl

. Teogene volc'anisrn in Fla"rghitn Lfts as well as in the whole Cdii-T?oi-Gurghiu-Ifarghita vcit'anic.rhain tcok place in two main stages:(1) a prevailing explosive stage during which the lowe" tol.uoic comp"art-ment. (the _volcano-serlirnentaiy f'orm6"tion in its peripheric,al parts)^ wasconstituted and (2) another nrainly effusiye stale fuilding ine actuatvolcanic e,difiees (upper volcalic compartment) of The axial ,lnos (Rd,du-lescu _et al-, 1981). Pioducts of the firit stage aro repr.esented by andesiticand clacitic fallout. tuffs, _p1'roclastic. fto; depssits, *,*l flbl' (iahar)cleposits and subordinatell hva florvs. Lava flor,is an,i d,-,rrres with rninorinterbed"ded pyroclastics, nlartrll' _andesitir: in cgmposition, constitutevolcanic structures resu-lted during the secontl stage of volcanism.al-,ocally(ciornaclul massif) explosivc volcanism pr.evailed''.

' { .vp-*al l l ' t 'nle-aikai jne r l l tm_llnr rrf gtrrtrat ing nragn}{ls irr the rnostpa,rt of volcanic ehain turn tc higli-1:ctlisiir. t,t,rrclciir..r' j i i South Harghitaelnd to sltoshonit i t 'cne in thcir soirthl ' rn rxtrtnri tv tSrstredi . t al . , f t)gO).

(J)(:{1uf r0[!tieFi

Yrllr:anitl bcmtrs rlrrd l;lacks in llarghita l\[ts occrlr, i' t,wo zone;1 :qtr) {)iornatlul ura,ssif anrl 12) casteln pari'of i\orth llars^hit,r ffn*,-i;;;iof l)itne,Tti (Irig. 1 ). In t,ht' fir st case, tliclX occur rvithin thE upper 'olcapicarclmpaltnreril, ilrrd ilr the second oncr wiihin tlre lowe, o.,i*aloic compart-nrent.

tr'. In Cicmadrt.l uiass,it knowrr l:crnl,s originated l'r,orn Krlgrlos6,rokl:r'ooh *- olt v*lt:l:,ltit'1,,113' r.rownstrccm ot ruqnaii-niri .- '"h;;;'theywere fiiuncl in the vaIlt'1'-hottcut detached fi 'onl *,'ht*3' |onsolidate4 pyr*clastic milttx'ial in rrhich tht'y \\'rle bu.r'ied. Tocilj- Jrr*i., ur* still fou.ndr{ome specirnens or fragrnents along the valley. -'u

Yolcanicr bcnibs ancl blcclqs are jar$etr), ftiuld jn neq,. occlu,r.enc.,e$in llorcului and Ltt,cltiti i Lrrccks cn thr srr;itxrn slcipr of the massif. IIer-'

VOLCANIC BOMBS AND BLOCKS IN IIARGHITA MTS

they ale met either detached from its matrix along the valley bottomarrd engutfed in a clayey block and ash deposit of a likely laharic nature.Surall specimens and bomb fragments are also found on northern slopein Benevize and Yalea Rosie brooks.

Fig. 1 - Geological sketch of Flarghita llts with volcanic bomb and blocli occurrenccs.

X, Quaternarl deposits ; 2, Upper volcanic compartment : rnassive volcanics (a), pyroclastics

(b); 3, Lower volcanic compartment : volcano-sedimentary formation (a), massive volcanics

(nl) ; 4, Neogene sedimentary deposits of Trarsylvanian Depression; g, Crystall ine-Nlesozoic

zone and Internal Flysch zone : 6, Crater; 7, Occurrences of volcanic hombs and blocks; (1)

Kornlosrirok brook, (2) Porcului brook (Ciomadul massif), (3) \\'est Dineqti.

183

"{.J"F"'L &, ,

' \ , v

/ r " , r f q'l

v v ./ ;t v Et i i#- 0 - - 3 0 :

0 \ (

0- A

qYI1

H oYtT' l$o'__:f_f_f*

[-__lr

E]q b

EEa b

==

mtr'a

I

- 0 - e -

- 0 0- 0^n- -0

0 [ \ r / 0 ^

184 AI. SZAKACS, CS. JANOSI

fn fact in all these occnrrences, bombs antl blocks represent, coarseelements in the mass of volcanqclastic deposits *'hi"tr f;nn t11te1,;;.fuutiocone around the well known Sfinta Ani, and Mohoq craters,^fiuilt in aflrgt explosive-eruqtion phase. The only situation-i.i *Ti"n ttre relationof bomb and bloek hearinq {eposit is ex$osed lPorcutui brooky tireir.ho*-tic ,structure, lack of bedclifg a_nd soiting is evident. Thq" oo^i,*t,-,itcentimetric and decimetric angular and s.iir^ngular Oacitie 1it,hic elastsin an ashy-clayelr uncorisolidited rnatrix. Voicanic bombs and blo*ksrepresenti"g some of these clasts are ehaotically includecl. No 6ornl:-sagsare found in the sufrjac-e1t fines. These obseriatlo"* p"int to the flol,ryorigin.of depcsit, rather laharic than pvroclastic, anil sulg*st a secondaryinclusion for bombs.

2.Tn th-e 'west D[neEti zone, volcanrc bombs and irloclis are fou"r:don an about 1 krnr,arcaalong Groapa Apei Vallt,y. upstrrunr tire con{1ic.nr-.ervith rlrasag.brook and on their siop.i (Brlutui'uiie surduc iili*f frrr.yoccur exclusively as isolatccl coarsb fragrnents along the yalle)' or onthe volcano-sedimsrtary platcau on an outcr op LacEing area. Most ofthem are gathered by peolle in h.urnmock,c for firr."-l"g-hayfieltls.

Local occuruence ancl large number of volcanic bJmbs and bloehs.some of them of great volume, suggest the r"elatively .roi*"*u*1;;il;(uo erup_tion centt't' r'espectiTell')

-liketrv brrried and situatecL inside thejower volcanic compar,tment.

Voleanic: Bonrb,s and llloeks

1. fn Ciomadul rnassif, volcariic bombs and blocks as most of vol-canies in this al'ea are dacitic il ccmposition (amphibole, biotite{pyroxene;fquartz daeites) (Szak6,cs, Seghecli, 19S6).

rf--1,._-te

1

{ '

J--*\-( ' :\-.*--i

6

-"4:.-'lr.-_-----J

1

--z'--'1/ ' \,.,/ \f j

,r _1; ' l

i " 1\r d.,

.-* It ' ' -_ -

- - . , - - - - ' " -

I

.4--.ri{

o'),

I -i.'r l r , ,1

Vt:I

It___

I.'ig. 1! .- Iforpholoi:;3- of rrolcanic bonrbs and bloclis irr Cionrathrl nrassif.

Their size vari t 's f i 'cnt 0.1 ---0,5 rn 1o {}.8 * 1.0 trr jn diamcrter.nnrost tlf thcln having.0.2 - 0.3 rn. I.{o significant si,rr. i,zrr{ation rvith tlis-laqce .frcrrr presuured sclurct' wzls obs.,r'vcd. This pliru.* t.irt,it. subseqrrc,ritjnclu,sion in vcleanoclastic 6qtr,sit.

S\ape is also variablc. iMost ate r:haract,erized b)' pol;'g6nal s1apo.rsometric.polygonal forms arr,. r'rrlatir;dv,rare, (lrl. r," figs. j., z).trdoebirequent flatt,ened pol.l'gonal forrns arci'fourici.'I,Iighl.1, ij,picai flir ci;_madul massii, aIe tvealilv flattcued polygonal sliet.irnon* .iitt pe,ntagonalor.^hexaganal'contour, usually navifg .i,ti u*y**etric transvtrsal .sectionwith a tlatter lower lialf a,nd mon: curvecl dpper hatf qfu. zy. Iles*lt.d

\IOL(-A}IIC I3OMBS AND BLOCKS IN HARGFIITA MTS 1 F 5

potygonal surfaces are weaklv curved,lnore frgeuent conr,ex, rare conc&veor tlat. There wer.e also forrnd y"11- 'ti"it"*A

forms, some of them withobiong polvgonal secrion (pl. rJrrFig. ?,"i,irr;1q-fi;'iffi;ngular 1F,ig. 2).A number of bombi and bloefts nu"u .rrif.T *;;gt" consisting ofi"Tf-1l1gt}*_)- crust,_ from several mm to 2 - 3 em thicl. Their interiorrB alwa)s porous and has a lighter eolour Jsrer) contrasting to d.ark-Ereymargins (Pl' -rrr' Fig. 2). Spe;cimens lacking ehilled *u"gi;,

"irJliin?'ii.colour. Their interndl stnet'.,re i_--u*uuit;Lassive, but oriented fluidaist*uctu'es' parallel to flattened. gluql ar*'atso i"ila iri. lr, Fig. z).The strectacular characteristic feature oit'-JrliiiJ^rro-bs and blocksin c'iomadril massif i.s bread-cnrs-t qrygking-. cracks uru Lrge, cleep and]e1,; cto1g-spaced in speeirrens rvith.hiu.d;argin 1pl. r, Fig. 1) and thevrorur a fine close-spaced shallol netu,ork in thlse i;;i.ilg. .iiu-Jiil.r.dt[il|,#lat'ft_1)

sometimes eracks shou, a surrparalltJiaer.eropmen; i;Some small bombs ]rar-e cltaractt'r'istic star-like irnpact cracks situa-tecl exclusir-ely on trre rnor€ c'r'r-ed sur"face 1pr. rrr, n!*. s, 1).2'rn the rvest D[neqti ar"ea, r'olcanic rrur'"ir., -ii,i rrr8it are andesiticin composition (pyroxene'andesiiur,- oilH"sio" - 6Loio: szak6cs, seghedi

3, ,

It

- -\rorp''olog)'of rolcanic bomSs a'cl blochs in rvest l)d'e;ti area.

irr lf{ureqan et al., 1986). Except.t;'pical specimens, they_ cannot Lre easil.yrecognized' Ilost of them rnar- bcl^confu$.1-ut tiiiti -lbrrl rvitl ortlinar.i,.subangula. andesitic fragnrents rvhich "ii*rii-

;;;;p;,4"'.our... volcani_cla;ts in this area. Their pol1'gonar siiape-ott.r, .vrith'-cur.red surfaces andedges, chilled margin or-inielr'al 'aoiit jointi"g,, l..l**.", recognisingfeaturcs at a more careful "xan

inaii;;: 't

lir. range is betrveen ferr decimenters to about 1.b m.Shapes ary p-ol;rgonal, limited,t y qlane or curved surtaces (F,ig. J).tSome tend to be sharper a{, one ena anh truncated at others _resemblingto tt shell (Pl' Yrr, Fig'. 2). Tt rvas found-a smalt"i "io"fured

specimen,

Irig. l3 - -\{orphologl. of

136 AL. SZAKACS, CS. JANOSI

pentagonai in section, rvith ,,pinch" at one end, thlpgi-nt where the ]romb

detaches fromlava. Iis aspect srrgg.sts atorpedo (P[. V, Fig*r 2,3)-' Gene-

;ffy prevail quasiisomefrical a-riO elongated shapes, flattened forms

loeing rare.Some bombs and blocks show breacl-crust cracks. Crack networ'}i

is more close-spaced- antl more superficial than_111 typicat bread-crust

cracked daeitic^bombs from Ciomaclirl massif (Pl. VII, F'igs.-l-,2-).Someti-mes crack system is ,,virtual" when poll'gonal and.esitic block breakes

al, hammer bits along"a zig-zag surfac*e. Sdveral specimen show internal

radial jointing (Pl. il, -{iS._ 2).R"arely #e'iound. bniU".O margins, 0.2-1 cm thick, shou'ing letluced

crystallinity with respect to the interior (Pl. YI' Fig. 1)' In most caije$

th-ere are no structural heterogeneities.

I)iseussions

In reler-ant literature, gent'rallv a clear concephtal disti-nction

bet.ween volcanic bombs aoci b-io.ks ii mad.e (Mac Donald, 7?7?; Fisher,

Schmincke, 1984). The forrner represents material ejected in molten

*tui" lesseritial ejecta), theil shape resulting through solidification dulirrg

aerian tr,ajectorf and'shortly laler. On the contrary, blocks are ejectecl

in solid state.nlith clefinitir,-e shape in the eje_ction rnoment. Therefole,g.*r"fiy the_v represent accesorl' o_r_ aecidental material, but blocks ean

ii*o orilinate as-es.et',tial ejeeth, (lfacl)onald, 7972). fn this last case,

distinction bet\yeen bornbs arrd blocks is not always possible due to feature

conYergencies.Bread-crust cracking lllaY occltr lroth in bombs and blocks' L-arge

ancl deep cracks or. trrotJ frequent in bombs and Jl"y are the result of

interior Oegasing' ancl the gase llressure caused breakllg of initially forme.el

at"*t. Suc[ boinb.* zrrL' charact*r'istic for more silieie, mainl;r dacitis

magmas.Blochs can also have bread-crust t)'pe cracks, shallor,ver and more

close-spaced but ther,e are all intermecliate t1-pes betrveen this-trvo aspects

iffl-.tlt"*0, fOZ2). l'or blocks, clacking riould result- by reheating, s'rt-

metimes up to incand.escence, _ of preexistent consolidated fragments.In Ciomadul massif, all these

-aspects are found. Specimensrvith

chiled. margin and deep bread-crust crdcks most tikgly are trombs. Those

of fine cracking and wiihout chilled. margin likely lgtq"g to bloeks. Bomb

versus block n"ature of several specimens rvith fluidal structure pointing

to a previous consolidation is highly doubtful. The same petrographical

eonstitution shows essential or at most accesory nature of fragments.

Different structural aspects suggest that expulsed material rvas in'variotls

consolid.ation states in^tUe erriplion moment. Disruption throrrgh a crust,

covered by growing lava dome*is a likely process for originatpg the des-

cribed boinbs and'blocks. Atternativel;i part of them Tay -be -not qP-

fi*lic*Uy .*pl"c.d and subse quently renioied -eje cta, but simply thermally

craked lava dome crust frafonenis included in ilorv deposits. Impact

cracked specimens are at least ballistic explosion products'

In west Dflneqti zone where massive valieties rvithout chillecl margin

predominate, mosi of described co&rse polygonal fragments seem to

VOLCANIC BOMBS AND BLOCKS IN IIARGTIITA MTS r.37

be blocks' Bread-crust features in several cases may originate in thermalcnacking of previously consolidated clasts. same petrographical featuroand evidence of detaching from partial unconso[dafudhaterial suggestthat tht.t are-essential and/or accetsory fragments, and presence of bombsis not ercludedBeeause an aceurate discrimination betrveen volcanic bombs and

llff *ii#tr#iidJ,fi ,*T','1,1hHT,1*"ffi:"f,"T;,"flT$i"i"x,fi["r#*lAcknowledgements

The authors are indebted to clr. s. pertz and dr. r. seghedi forcritical lecture of the manuscript and tor perti"*ot *sgotions in the textimprovement.

a Although the presence of volcanic bombs in south cil inrani IIts rvas mentioned (peltz,L969;, there are no observational data (occurrence, description) about them. Long time thevolcano-sedimentary formation in c{iimani-Gurghiu-Harghita volcanic chain was erroneouslycollsidered to be mainly constituted of agglorneraies, i.e. volcanic bomb deposits, rvit.houttrlreiJenting real cases.

ITEFEITENCES

Bftayai J' (1964) A szent Anna tavi ikcrlir{tcr crupci6j6nak kora. Fdld rajzi Erteslto, xIII,t , p. 57-68, Budapest .Fistrrer R' \t ' ' Schmincke H.u. (1984) IJl 'roclastic I--toclis. Splinger verlag, Ilerlin, l leidelberg.

Nclv York, Tokyo, 472 p.I'facDonalcl G' A' (L9721volcanoes. Prentice IIall Inc.. I inglervood cliffs, Nerv Jersey,510 p.Mihnild N', Peltz s', \ 'onrrer F. (1972) f)ate uoi privind depozitele cuaternare ;i vulcanismul

bazaltic ditt regiunea Floghiz-\'enefia (mun{ii Pcrsani). st. teltn. econ., seria }r4, p. 69-93, Bucuregti.

Peltz s' (1977) contributii la cutroast,erca aparatului l 'ulcanic Ilegheg (Raco;u de Jos -\ {un! i i Perqa' i ) . D. s. Inst . Geor. Geoftz. , I .x I I I (1926), p. 69-g3, Bucureqt i .

niure;an 1I', Mureqan G., Kriiutner II.. I ir i iutner F., szakricsA., seghedi I., peltz S., BratosinI' (1986) Report, the archives of thc Institutc of Geology and Geophysics, Bucharest.

Peltz S' (1969) Studiul petrografic al pirfi i cle sud-est a munfilor Cilirnani. St. tehn. econ.,seria I, 4, p. 3-206, Bucuresti.Ric lu lescu I ) . , Borcog $I . , pel tz S. . Is t rate G. (1gg1)

Carpathians. Carp. - BaIk. Geol . - \ ,soc. , XI I132 p .

Subcluction magmatism in RomenianCongr., Guicle to Excursion, Bucharcst.

SoutheasternmostRea. Roum. G6ot.

seghedi I . , Grabar i G., Ianc R., f inr isescu A. , v i jc lea E. (1986) nb, Sr, Zr , - f , . , u, K in

tlre Neogene Yolcanics fronr the South Ilarghita l lountains. D. s. Inst. GeoL Geofiz.,LX \ -LXXI / I (1993_1984) , p . 1b l t_4b2 , Bucures t i .

Szak{cs A., Seghedi I. (1986) Chemical Diagnosis of gre Volcanics frorn thePart of the Harghita l\Iountains - proposal for a New Nomencrature.G6ophgs. G6ogr., Giologie,30, p. 41_4g, Bucuresti.

1q8 AL. SZA}<ACS, CS. . IANOSI

EXPLANATION OF PI-..ATES

Plate I

Fig. 1 - euasiisometric polygonal volcanic bornb, rvith chilled margin and hread-crust clacks'

porcului brook, Ciomadul massif. Collection of Harghita District lUuseum, Miercurea

Ciuc.

Fig. 2 - Isometrie polygonal volcanic bomb with chilled margin and bread-crust cracks' Por-

cului brook. Ciomadul massif. Authors' collection'

Platu ff

Fig. 1 - Flatty polygonal volcanic bomb lvith chillecl margin and breacl-crust eracks- Porcului

brook. Ciomadul massif. Collection of llineralogy Departnent in tsiology Geology

ancl Geography Faculty, University of Bucharest'

Bo}fBE VI]I,CAN ICE r}I\ },IUN TII }IAR GFIIT.A

( Rezumat )

pe ling6 ocurenta cunoscutI. din piriul Komlosfrok, bombc' vu-lcanice

apal,, in nlmdr mare, in valea piriului Polcului de pe_ \:er',santul sudic aI

"i"*ii"f"i biomaaul. Bombele

-sint inglobate seoundar intr-un depuzit

vulcanoclastic haotic cu blocuri ;i liant cineritic-algilos, tle natuli, 1'.1*

haricd,. Compozi{ia lor este clacitic5,. Bombele, d"- dinensiul}i \-ariabile,i" g'"".tal dicimetric[,, au torme Yariate, de reggli Poligonale, cele nrai

caracteristice fiind uqcir aplatizate, cu o palte-(lnferioard,) mai !.;itfi, ,:ialta mai bombat5. Majorif ate^ au o margine hialind, qi cr5pd,turi {9 tip

;e"-tt Ou piitt.". S-au" intilnit qi mici bombe cu cr5,p5,turi radiar-diver-gente,^ de impact.'in

munlii Harghita d,e Nord, intr-o zond,la vest de comuna D_[neqti'

au fost identificate" la suprafa{a terenului bombe vulcanice andezitice

in aria de dezvoltare a forinaliunii r.uleano-sedimentare. Ele silt -poliSo-nale, adesea cu fe!,e ;i muchii curbate. LTnele au o margine cu cristalinitate-ui'r.6",*e. git.oOite prezinti, o cnrsti, cu crd,pd,turi de tip ,,caaJd' cle

pi inet t .ln literatura cle specialitate se face distinc{ie intre bombe qi bloci-ui,

ultimele repr.ezentind ejcclii in stare solidd,. )Iajoritatea exemplal'enor

din masivui Ciomaclul se incadreazd,Ia bombe, dar-in cazul unui numfr

.1. ut.*plare atribuirea tra bombe sau blocuri.este inct'rt5,,da!91it5'-:f:i-tenlei fdrrnelor d-e trecere. Aspeclele morfo_logice qi structural-texturaleobservate denoti st[ri variat^e de consolid.aie a

-magrnei in momentul

erupliei. Originea bombelor prin tlisruplie printr-un d.om sau lac de lavfl

cu 6 crust5, in cut* cle solitlit'icare este cea mai probabild,.ii ronade la vtst de l)irrre;ti, rnajoritatea exemplarelor, pril carac-

terele lor, par szi apartin.i bloeurilor,,-deryi unele preziLt3t evidenla taptulur

ci, in momentul eipui zdrii nu sc ailau- in stare solidd,. Din acest motivqi pentru a e.i.ita utrdl. confuzii,.s-a preferat folosirea termenului de "borntrevrilcaniee" pentru toate ejecliile grosiere descrise.

VOLCANIC BOMBS AND BLOCKS IN HARG}IITA MTS 189

Fig. 2 - Fragment of flattened polygonal volcauic bomb or block with bread-crust cracks andfluidal structure. Porcului brook, Ciomaclul nrassif. Collectlon of the Geology andGeophysics Institute, Bucharest.

Plate II I

Fig. 1 - Flattened voleanic block with a fiue network of shallorv bread-crust type cracks. Por-cului brook, Ciomadul massif. Authors' colleetion.

Fig. 2 - Sectioned flattened polygonal volcanic bomb witir chil led margin and breacl-crustcracks. Note the porous $tructure of interior. Porcului brook, Ciomadul massif. Au-thors, collection.

Figs' 3, 4 - Small volcanic bombs with impact cracks. Porcului brook, Ciomadul massif.Authors' eollection.

Plate IY

Fig. 1 - Snrall volcanic bombs and bloclis and flagments. Porcului brooli, Ciomadul massif.Collection of the Geology and Geophysics Institute, Bucharest.

Fig. 2 - Flattened polygonal volcanic bomb uith breacl-crtrst craclis. Porculur brolrr, Ciomadulrnassif. Authors' collection.

Plate V

Fig. 1- l ,a lcra l v icrr of l . rornb i i r p late I \ ' . f ig .2.Fi . , -s . 2, l3 - Elongatecl polvgotra l r ,o lcat t ic bomb: notc the detaching "pi r rch" at one end.

Groapa Apci brool<, r rest i )dncst i . Authors, col lect ion.

Plate VI

F-ig. 1 - Nattrrally sectioned compact pol-v*gonal volcanic block. Note less crystall ine rnargi-nal bancl. B5{ului hill, rvest Dinesti.

Fig. 2 - Naturallv sectioned compact, curvcd faced volcanic block uith raclial internal join-ting. Groapa Apei brook, rvest Dinesti.

Phte Vff

Fig' 1 - Polvgorral volcanic block or bonrb with fine bread-crust cracks. Groapa Apei brook,west Dinegt i . ;

Fig. 2 - Shell shaped volcanic bomb with bread-crust cracks. Groapa Apei brook, west Dinegti.collection of the Geology and Geophysics Institute, Bucharest.

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AL. SZAKACS. CS. JANOSI. Volcanic Bombs and Blocks in Harghita Mts.PI. VII.

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