An update study in micro inclusions o f emerald from worldwide significant deposits

V N Ư Jo u rn a l o f Science, E arth Sciences 28 (2012) 230-240 An update study in micro-inclusions o f emerald from worldwide significant deposits Le Thi Thu Huong* Faculty o f Geology, VNU University o f Science, 334, Nguyen Trai, Hanoi, Vietnam Received iO November 2012 Revised 10 December 2012; accepted 26 December 2012 A bstract A conclusive study of inclusion in schist-type emeralds from some famous deposits in the world is introduced The deposists includes Santa Terezinha, Socoto, Capoeirana, Itabira (Brazil), Mananrary (Madagascar), Transwaal (South Africa), Ural (Russia) The typical inclusions for emerald of these localities are quartz, mica, amphibole, fluid inclusions Particular and unique features of inclusion could provide information of geographic orgirin Itabira emerald is featurelized with the abundance o f multi-phase inclusions containing two liquids, developed in well-formed negative crystals; more or less square, rectangular cavities Santa Terezinha deposit is charactierized with pyrite inclusion which is not found in other deposits Keywords: Inclusion, Brazil, Ural, Madagascar, South Africa, emerald 1, Introduction identfy not only betw een schist and non-schist l>pes but also am ong geographic orgins o f A com parative study in inclusion between gem stones in m any cases schist-type and non-schist type beryl has been pulished by the author (H uong, 2012) [1] M aterial and m ethods B ased on the inclusion suits a gem m ologist could identify from w hich m ine/deposit a For this research, gem stone originated, i.e schist type or non- 179 natural facet-cut schist type This paper introduces an update and em erald sam ples have been investigated in this conclusive study in inclusion o f the m ost study The sam ples w ere collected from Brazil favourist gem s o f this group, i.e em erald, from (C am aiba, Itabira, Santa Terezm ha, Socoto), som e w orlw ide fam ous deposits Follow ing the M adagascar (M ananjary), Russia (Ural), and form er study (H uong, 2012) [1], observations South A frica (Transvaal) All em erald samples from this study leads to the conclusion that studied belong to schist type inclusion features can provide inform ation to The inclusions w ere firstly observed, described, and classified using a gemmological m icroscope w ith Zeiss optics Then all o f the ‘ Tel: 84-0912201167 E-mail: lctth@vnu.edu.vn different types o f inclusions were photographed 230 231 L.T.T Huong / V N U Journal of Science, Earth Sciences 28 (2012) 230-240 and determ ined using confocal-Ram an 5000- specfroscopy All host em erald sam ples were polished at tw o parallel sides w ith the thickness 4000- varying from m m to mm The experim ents 3000- :i determinm g inclusions o f em erald were earned out on a LabR am confocal m icro-Ram an- 2000- I system HR-800 equipped w ith an O lym pusBX41 by JO BIN YVON H ORIBA I ‘ I /Í 1\ 1000- For 1»>* 0- searching inclusions as well as m easuring a 200 400 certain point, an objective w ith a 50 times m agnifying pow er and green laser 600 800 1000 1200 1400 1600 1800 W av e n u m b e r(cm '^ ) light (514.532 nm) w ere used R am an spectroscopy is a non-destructive technique to identify not Figure lb Raman-spectrum obtained from chromite inclusion in Santa Terezinha emerald only solid but also fluid inclusions in gemstones C hrom ite the in em eralds from the Santa T erezinha deposit They are listed as chrom ite, pyrite, calcite and O ther m inerals that we considered as typical inclusions are hem atite, feldspar, black rounded ones form iư eg u lar clouds or frails parallel to M ineral inclusions are found to be abundant am phibole, as individual crystals are isolated, and the small 3.J Santa Terezinha (Brazil) goethite, present crystals or in octahedrons (figure la) The big Results and discussion tw o-phase inclusions is quartz, and basal colourless faces to Carbonate brow n, m inerals irregularly are bordered grains, found either singly or in groups They w ere determ ined by Ram an m icroscopy to be calcite, dolom ite, hydrozincite and magnesite (figure a) m agnetite Pyrite inclusions norm ally occur as sharp or slightly rounded cubes T hey can occur solitaire or in groups N um erous m inute crystals m ay form tiny clouds iJ, , tí _ W- ^ Ẵ ỹ '*' Figure 2a Magnesite (MgCOs) in Santa Terezinha emerald x50 Figure la Chromite inclusion (FeCr 204) in Santa Terezinha emerald as a well shaped octahedron x50 L.T.T Huong / V N U journal ofScierice, Earih Sciences 28 (2012) 230-240 32 3.2 Socoto (Brazil) 25000- The great variety o f different mineral inclusions is found to be the m ost characteristic feature o f w hich m ica is the m ost frequently I 100ÍX)- observed inclusion M icas are usually biotite and phlogopite, and less frequent they can be 5000 m argarite or m uscovite This IS due to the fact Ỏ 2Ỏ0 4Ỏ0 6Ỏ0 8Ỏ0 1000 1200 1400 1600 1800 Wavenumber(cm'^) that the largest portion o f the Socoto em eralds is found in a b io tite /p h lo g o p ite schist h o st rock Figure 2b Raman-spectrum obtained from magnesite in Santa Terezinha emerald Talc m inerals are colourless, transparent to N onnally, the m ica crystals occur in the form o f ro unded colour o r irre g u la r-sh a p ed is generally and light p latelets T h eir to m u sco v ite dark are brown w hite or silky, in flake-like shapes (figure 3a) M argarite p ractically T hey are som etim es gathered in agglom erations colourless M ica crystals rarely occur isolated, ủiat make tìie ciystals appear cloudy Mica inclusions m ostly th ey fo rm w ere determ ined to be biotite as brow n flakes agglom erations o f m ica that som etim es m ake agg lo m eratio n s It is the the host em erald crystal have dark brow n colour (figure 4) and p a rtially a p p e ar alm ost opaque Sometimes, tubes are observed orientated in the direction o f the c-axes and are accom panied with m ica (figure 5) A part from mica, chlorilc inclusions are observed, w hich are som etim es not distinguishable from m ica w ithout the help o f confocal-R am an m icroscopy Figure 3a Talc flakes usually are very small aggregates in Santa Terezinha emerald, the big one as shown in photo is very infrequent x50 8000 7000 6000 5000 ệ I 4000 3000 rr^ 2000 ỈỊ 1000 : Mm Ó 2Ỏ0 400 600 800 obo 1200 1400 1600 1800 Wavenumber (cm'^) Figure 3b Raman-spectrum obtained from talc inclusion in Santa Terezinha emerald Figure Only rarely isolated occuưing mica crystals, usually forming agglomerations, darkening the crystal x50 233 L.T.T Huong Ỉ V N U ]ourna\ of Science, Earth Sciences 28 (2012) 230-240 • Figure Fissure system parallel to the c axis in emeralds from Socoto xio fậ Figure The dark brown core zone is caused by the conglomeration o f mica and some carbonate minerals x50 O ther inclusions found in Socoto em eralds O bservation in all sam ples indicates that the are actinolite, trem olite, apatite, talc, quartz, albite, m olybdenite and hem atite/goethite/ lepidocrocite, in w hich m olybdenite is least frequently observed and considered as a rare mineral inclusion Actinolite/ừemolite sometimes fonns thick needles or rods that are practically colourless and ừansparent T hey norm ally occur isolated but som etim es are found to be bundles o f num erous crystals show ing no p refeư ed orientation Besides the colourless, ansparent crystals, others o f greenish to light brow nish crystals occur that som etim es show characteristics o f a bam boo-like appearance the im portance o f actinolite/ừem olite as m ineral inclusions falls clearly behind that o f m icas The appearance o f isolated albite crystals and o f fractures filled w ith feldspar in the em eralds can be explained also by the fact that the Socoto em eralds are partly found in feldspar m asses H em atite occurs as sm all, irregular C ĩ7 sta ls that can fissures or be found m ostly w ithin dispersed over the surface o f the em erald crystals Lepidocrocite can be found som etim es to be associated w ith hem atite and shows a veiy strong red colour (figure ) A patite occurs as prism atic crystals that are som etim es slightly corroded and rounded They are colourless and they alm ost alw ays show cleavage planes parallel to the basal phase B ased on their appearance w ithin the em erald host crystal we can define them as protogenetic inclusions B esides the m ineral inclusion m entioned above, there are talc crystals occuư ing in the form o f ừansparent, colourless platelets A ccording to Schw arz et al (1990) [2], Eidt and Schw arz (1986) Figure Lepidocrocite (FeOOH) with very intensive red colour, with brownish hematite (Fe 203) x50 [3], tourm aline and orthite can be observed as rare inclusions in em eralds from Socoto also T he core with darker colour is caused by the high inclusion density, in genera], L T T Huong / V N U Journal o f Science, Earth Sciences 28 (2012) 230-240 234 they are dark brow n m ica, and m ay be carbonate m inerals, or others T he presence o f zonation (figure 7) shows that the grow th process o f Socoto em eralds is characterized by the repeated abrupt alterations o f the forming environm ent 3.3 C apoeirana (Brazil) T his study brings out quartz, m ica (biotite) inclusions in em eralds from C apoeirana Quartz inclusions are colourless, ữ ansparent, and can Figure Group o f quartz grains in Capoeirana emerald, xio be found either as rounded grains or in long prism atic form s R ounded quartz grains were found usually in groups, distributed iưegularly w ithin host crystals (figure ) Long prism atic /.■'I, '" " àiViỉSM quartz crystals w ere found as singly transparent ones, orientated parallel to the c-axis In some cases, quartz w as found to be associated with fracture system s or liquid inclusions M ica inclusions w ere found less frequently than quartz N ot only in one sam ple but also in the w hole sam ple set, quartz inclusions are more abundant than m ica M icas w ere observed as transparent brow n to flakes ừanslucent and slightly booklets or Figure Liquid inclusions in negative crystals in emeralds from Capoeirana x50 greyish som ew hat 3.4 Itabira (Brazil) rounded grains and they are n ot distributed in any certain p lace inside the host crystal In These em eralds from are easily found as atypical m ineral inclusions from this distinguished from those from Santa Terezinha region In the study o f Epstein (1989) [4], the and Socoto based on inclusion features U nder slightly w hite the m icroscope Itabira em eralds w ere found to crystals w hich w ere determ ined as calcite and contain relatively few types o f inclusions The greyish dolom ite w ere also found in a few cases W ell- general, those C apoeirana anslucent in like addition to m ica and quartz, siderite crystals are rounded, and are m ost frequent observed m ineral inclusions are form ed negative crystals together w ith two- quartz and m icas O ther m ineral inclusions, phase inclusions are another particular feature w hich w ere found m uch less frequent, are o f em eralds from C apoeirana (figure 9) apatite, em olite and hem atite A ccording to Schwarz (1987) [5] andesine m ay also be found Liquid inclusions built the m ost abundant group in Itabira em eralds w hich exhibit a large variety o f form s T his indicates a com plex and m ultiphase form ation history o f em eralds in this L T T Huong / V N U journal of Science, Earth Sciences 28 (2012) 230-240 region A m ong liq u id in clu sio n s, tw o-phase type (liquid-gas) seem s to occur more often They are widely and iư egularly disfributed within host crystals, and can be observed in various-sized tubes or in alm ost rectangular bordered cavities as w ell as in m ore or less perfectly form ed negative crystals Three-phase inclusions were som etim es found, and differently, they are usually com posed o f two fluids and a bubble (figures , 11 ), in case o f four-phase inclusions, liquid phases are still dom inant; liquids, a solid, and a bubble The type of liquid inclusion containing solid substance is occasionally observed in Itabira em eralds In general, liquid inclusions are so small that all attem pts to determ ine their phases by confocal-R am an spectroscopy failed Figure 10 Almost rectangular bordered cavities filled with two or three phase inclusions in Itabira emeralds, xio 235 A m ong m ineral inclusions o f em eralds, micas w ere dom inant They vary in a large diversity o f forms and colours N ot only does the colour o f m ica inclusions vary from sam ple to sample but also w ithin the sam e sam ple itself The colour m ay be com posed o f various shades o f brow n, from yellow ish, grey to dark brow n The m ica flakes are usually strongly rounded or iưegular In some sam ples, m icas are elongated or have a disc-shaped form and are (OOl)-oriented parallel to the basic face (001) o f the em erald The strongly rounded m icas w hich show no prefeư ed orientation are considered as protogenetic inclusion and often possess a deep brow n colour The thickness o f mica slabs are also very different, som e mica slabs are so thick that they appear alm ost opaque and show very clearly cleavage surfaces (figure 12) A nother appearance o f protogenetic mica is that the mica crystals are in a state o f dissolution (figure 13) The syngenetic m icas are m ostly thin and transparent flakes w hich are either elongated or partly exhibit a distorted pseudo-hexagonal shape These flakes show the following orientation w ithin host crystal: the elongated crystals lie parallel to the c axis, and the pseudo-hexagonal crystal lie parallel to the basal plane M icas have been d eten n in ed by Ram an spectroscopy as biotite and phlogopite Q uartz is another type o f frequently observable inclusion, b ut m uch less frequently than mica Q uartz crystals occur norm ally colourless, elongated or rounded and som etim es are found to be associated w ith liquid inclusions A nother type o f inclusion in Itabira em eralds are various fissures w hich rem ained unhealed This indicates that these fissures were formed w hen the crystal grow th process had been stopped, thus the crystal had no longer contact w ith any liquid environm ent In a few samples, trem olite, apatite and hem atite are Figure 11 Multi-phase inclusions were found often containing two liquids and gas x50 rarely found 236 L.T.T Hỉiong Ị V N U Journal of Science, Earth Sciences 28 (2012) 230-240 Q uartz inclusions are m entioned in almost all em eralds from different localities [ ] In M ananjary em eralds, quartz appears in a diversity o f m orphologies Q uartz inclusions can appear as transparent, colourless, elongated (or pnsm atic) parallel to the c-axis o f the host em erald crystals, often associated w ith primary fluid inclusions (figure isolated crystals, 14) They occur as irregularly distnbuted throughout the host crystal or dispersed over the Figure 12 Thick brown mica flake with cleavage or growth surface x50 planes o f healing fissures The others are postgenetic inclusions that show iưegularly rounded crystals, som e o f w hich have a badly '.m ' coư oded rough surface Figure 13 Mica flake with corrosion x50 3.5 M ananjary (M adagascar) A bundant types o f m ineral inclusions are the m ost striking internal Figure 14 Quartz appears with fluid inclusions in prismatic form x50 characteristic observation in M ananjary em eralds M ost o f the inclusion features are sim ilar to those found in em eralds from other schist-type deposits N evertheless, n ot all o f M ananjary em erald inclusions can be found in any other locality T he association o f num erous m ineral inclusions such as am phibole quartz, m ica (actinolite, (biotite, phlogopite), trem olite) and other m inerals such as feldspar (albite, oligoclase), carbonate m inerals (m agnesite, calcite, dolom ite), talc, m olybdenite, tourm aline and fluid inclusions is a special feature o f em erald from this occuư ence Figure 15 Thin plate o f mica inclusion in M ananjary emerald x50 237 L.T.T Huong / V N U Journal of Science, Earth Sciences 28 (20Ĩ2) 230-240 Ọuartz inclusions can also be observed in in em eralds; the observed am phiboles are groups o f small grains T hey are well rounded actinolite and trem olite They arrange as chaotic or the tubular crystals w hich always knil w ith others appearance o f m ica inclusions in M ananjary But that disừibution o f am phibole is only in emeralds is even m ore frequent than that o f certain areas o f the host crystals, not in the quartz T hey belong to the m ost com m on group whole o f mineral inclusions M icas w ere determ ined Habachtal almost spherical N evertheless, sample as those in em eralds from by Raman spectroscopy to be usually biotite In com parison w ith the above m entioned and phlogopite They often appear as thin plats inclusions, carbonate m inerals, feldspar and with usually som ew hat rounded edges, or may m olybdenite also have a alm ost perfect sharp outline (figure m inerals are m ost iư egular or rounded grains, 15) although they are less show frequent some C arbonate relatively w ell- developed rhom bohedral crystals In general, they appear ansparent and colourless The surface corrosion m ade some carbonate crystals appear slightly brow n Feldspar is determ ined norm ally to be either albite or oligoclase T hey are usually iư eg u lar in shape and often very rounded or co o d ed (figure 16a) M olybdenite occurs as grey or silver platelets w ith typical m etallic luster T hey may be slightly rounded or show Figure 16a Oligoclase (KAlSisOg) found to be with two-phase inclusions x50 a well developed hexagonal outline Tourm aline has been reported in M ananjaiy em eralds by other studies ([7], [8 ]) H ow ever, according this study, tourm aline belong to rare 1800- inclusion 1600- caterogy of M ananjary em erald (figure 17a) 140012001000- 800600 400- ii-' ^! 200 200 400 600 800 1000 1200 1400 1600 1000 Wavenumber (cm*^) Figure 16b Raman-spectrum obtained from oligoclase inclusion in Madagascar emerald Not only m ica schists are host rocks o f em eralds in M ananjary but also am phibolite schists (although less frequent) C onsequently, am phiboles also belong to the m ain inclusions Figure 17a Occasional case o f tourmaline crystal found in emeralds from Mananjary x50 L.T.T, Huong / V N U Journal of Science, Earth Sciences 28 n o i l ) 230-240 238 the prefeư ed orientation in host crystals parallel 1800- to the c axis 1600- Growth 1400- ^ 1200- § c zoning is another feature of em eralds from Transvaal They alm ost appear 1000 - as fine-scaled parallel lines (figure 18) The 800 600- colour betw een the lines IS slightly varying 400- This indicates that the form ing environm ent o f 200- Transvaal em eralds w as not harshly changed 00 200 400 ' 6Ỏ0 ' 800 H em atite and lepidocrocite w ith the typical red 1000 1200 1400 1600 1800 colour were found com m only (figure 19) W avenum ber (cm‘^ ) Figure 17b Raman-spectrum obtained from tourmaline inclusion in M ananjary emeralds 3.6 Transvaal (South Africa) As em eralds Transvaal hosted em eralds in biotite schist, the typical present inclusions for this origin: fluids and mica (biotite, m uscovite) as well as atypical ones such as calcite, quartz, talc N otably, fluid inclusions in Transvaal em eralds were found few er in com parison w ith m ineral inclusions in Figure 18 Growth zoning in emeralds from Transvaal X Ỉ O one sam ple itse lf or in com parison with those in other localities o f the same host rock (for instances, Itabira) These appear usually to be sm all, containing two phases, a liquid (w ater or liquid CO 2) an d a C O bubble Som etim es, they can be seen in elongated cavities Liquid inclusions in veil-like type or in tubular fissures w ere also seen T hese m ake groups of irregularly shaped tiny inclusions w hich look like curved veils This type o f inclusions has also been observed in “em erald” crystals grown by the flux m ethods, w hich w ill be m entioned Figure 19 Lepidocrocite, with light brown flakes o f mica x50 later in the part on synthetics 3.7 Ural (Russia) M icas are considered as the m ost frequently observed inclusion, as been described in many localities; they appear w ith typical brow n These em eralds several types of w ere liquid found to contain and two-phase colour C alcite and quartz show m ore or less inclusions The w ell-form ed crystals Q uartz crystals present the form o f flat cavities orientated on planes mOvSt notew orthy were found in 239 L.T.T Huong / V N U Journal of Science, Earth Sciences 28 (2012) 230-240 parallel to the pinacoid In general, exừem ely thin channel-like sfructures running parallel to the c-axis, that IS, perpendicular to the flat cavities, are confined to these planes These cavities consist o f liquid or tw o-phase (one liquid and one bubble) inclusions and they have less frequently three-phase inclusions C hannel­ like grow th tubes parallel to the c-axis and elongated fluid inclusions trapped on grow th planes w ere observed In addition, num erous, partly healed iư egularly fractures fra versing w ere through observed m ost crystals Figure 21 Elongated mica inclusion in Uralian emerald x50 o f the / In a few cases, fluid inclusions in Uralian M ineral inclusions w ere found only rarely em eralds were found to be alike w ith those in em eralds from Itabira: three-phase inclusion containing liquids and a gas bubble Thé gaseous and liquid phases in these inclusions are CO The solid phase in three-phase Iiiclusions is halite, but the halite crystals found here are not in the cubic fonn as those in Chivor or G wantu em eralds The feature o f clouds or trails caused by tiny particles found in C am aiba em eralds w ere also found in U ralian em eralds (figure 20) As described, these particles are the tiny one or tw o-phase liquid inclusions that make the host crystals look partially translucent only in U ralian em eralds The m ost frequently observed m inerals are several form s o f m ica w hich were determ ined by confocal-R am an specfroscopy as phlogopite (and m uscovite w ith the sm aller portion) w hich are know n to originate from m ica schist host rocks In general, phlogopites are virtually colourless, only a few o f those show the brow n hue N onnally, they appear as the m ore or less coư oded flakes w hich are considered to be the typical form o f m ica B ut som etim es they can appear as sm all rounded grains w hich at the first glance look like quartz grains In other cases, the elongated fo n n m akes them to be confused w ith am phibole (if rem em bering that am phibole schist is one o f the host ro cks o f these em eralds) (figure 21) N evertheless, true grains o f quartz and actinolite also occur A ctinolite crystals are found usually to occur individually D ue to the m uch less frequent appearance o f m ineral inclusions in com parison w ith liquid ones and the features o f liquid inclusions, U ralian em eralds p resent them selves to be m ost alike w ith em eralds from C am aiba Figure 20 Tiny particles (fluid inclusions) in Uralian emeralds resembling those in emeralds from Capoeirana x50 240 L T T Huong / V N Ư Journal o f Science, Earth Sciences 28 (2012) 230-240 C onclusion loaning sam ples and providing research equipm ents for the research B ased on the study, it leads to conclude that the inclusion suit o f quartz, m ica, am phibole, fluid inclusions are norm ally abundant and R eferences considered as the typical inclusions for em erald o f all o f study localities In m any cases, with the keen eyes of experiences, [1] inclusion observation could help not only distinguish m ineralization conditions betw een schist type and non-schist type em eralds but also identify geographical origins o f particular sample The feature o f abundant containing tw o m ulti-phase inclusions liquids, developed in well- form ed negative crystals; m ore or less square, rectangular cavities is characteristic for Itabira beryls Beside the typical m ineral suit, there are the individual m inerals that exist only in certain localities and could be a great value to lim it the range o f beryl location, for instance, pyrite is found only in Santa T erezinha (Brazil) Centre for G em stone R esearch at JohannesU niversity is acknow ledged (2012) [2] D Schwarz, T Eidt, A Couto, The Brazilian emeralds and their occurences: Socoto, Bahia Journal o f Gemmology, 22 (1990) 147 [3] T Eidt and D Schwarz, Brazilian emeralds; inclusions and genetic aspects; Socoto and Camaiba, Brazil Fortschritte der Mineralogie, 64 (1986)41 [4] D.s Epstein, The Capoeirana emerald deposit near Nova Era, Minas Gerais, Brazil Gems ã Gemmology, 25 (1989) 150 [5] D Schwarz, Brazilian emerald occuưenccs and characteristic properties of Brazilian emeralds International Gemmoỉogicaỉ Conference, (1987)41 [6] D Schwarz and Ư Henn, Emeralds from Madagascar Journal o f Gemmology, 23 (1992) 140 A cknow ledgm ents G utenberg L.T.T Huong, Micro-inclusion study in beryl: A comparison between schist type and non­ schist type, VNƯ Journal o f Science, 28, for [7] H.A Hanni and H.H Klein, Bin Smaragdvorkoinmen in Madagaskar Zeitschrift der Deutschen Gemmologischen Gesellschaft, 31 (1982) 71 [8] D Schwarz, Emeralds from the Mananjary region, Madagascar: Internal features Gems ỔL Gemmoỉogy^ĨQ2{\99A)%%  ... m ineral inclusions in Figure 18 Growth zoning in emeralds from Transvaal X Ỉ O one sam ple itse lf or in com parison with those in other localities o f the same host rock (for instances, Itabira)... inclusions o f em eralds, micas w ere dom inant They vary in a large diversity o f forms and colours N ot only does the colour o f m ica inclusions vary from sam ple to sample but also w ithin... observation in M ananjary em eralds M ost o f the inclusion features are sim ilar to those found in em eralds from other schist-type deposits N evertheless, n ot all o f M ananjary em erald inclusions