The chemical composition of glass in Ancient Egypt

Introduction
It was only during the time of the Romans that glass became common place in the Mediterranean world. The people of the preceding periods considered its function to be decorative rather than utilitarian. Glass in the ancient world usually appears in the form of semi-precious stones made from materials as various as turquoise (pale blue glass) and fluorite (purple glass) (Freestone 1991). The precious quality of glass is captured in references from Mesopotamian cuneiform texts to “artificial lapis lazuli”; lapis lazuli is a gemstone that originated in Afghanistan and was traded as far afield as Ancient Egypt. Glass in the ancient world was manufactured by melting a combination of an alkali (potash or soda) and silica (raw materials such as quartz cobbles and sand). The interaction of the heated soda and the hot sand would have formed a transparent flowing liquid that the ancients then permitted to cool to form glass (Freestone 1991). It was the ancient production of metallurgy and faience that are currently believed to have resulted in the later manufacture of glass. The Bronze Age of the Mediterranean was synonymous with vast quantities of differential metallurgical processes. The slag by-product of such workings was a glassy-like material. The ancient beads that have been analysed shown to be composed of a high percentage of such by-products back up this hypothesis. Faience consists predominantly of crushed quartz and finished off with an alkaline glaze into a ceramic body (Freestone 1991).
Glass is a non-crystalline material that is, in essence, a super cooled liquid and not a solid. It is characterised as such because of its ability to liquefy “at a much lower temperature than that required to manufacture it� [Its] rigid metastable solid [is] produced by cooling the liquid form rapidly enough to prevent crystallisation, the stiffening occurring predominantly at the glass temperature. It is characterised by an arrangement of atoms or molecules which is irregular, and thus contrasts with crystalline order� The art of glassmaking combines two distinct, independently evolving, technologies, the development of pneumatically drafted furnaces and the invention of glazes. Technically, faience, glass and vitric ceramic ware are related, in the high temperatures are necessary for their manufacture, similar raw materials are involved and all are vitreous to varying degrees.” (Saitowitz 1996)
Until relatively recent times, the alkali component of the glass as well as part of the sand would be preheated and fused together before they were combined with the final components. Therefore, glassmaking consisted of two distinct stages: the raw materials were first fritted and then the melting occurred. The initial fritting process expunged unnecessary gasses and helped the subsequent melting. Commonly scrap glass was incorporated into the raw material mix with the aim of accelerating the fusion (Saitowitz 1996).
The production of glass requires several pre-requisite factors: a pneumatically drafted furnace with the ability to produce concentrated heat of between 900 – 1 000 degrees centigrade; the temperature reduced inside the furnace to that required for vitrification by means of the introduction of an alkaline flux; “a first firing of the mixture of granulated silicate and raw materials resulting in the production of a frit at a temperature of about 750 [degrees centigrade;] a second firing at a higher temperature of about 1 000 [degrees centigrade]. This firing requires sustained temperatures over lengthy periods of time. Complete vitrification can take many days to achieve; in order to speed up the vitrification process, cullet is added to the batch. Cullet acts as a catalyst in the process of liquefaction into a homogeneous mass.” (Saitowitz 1996)
Reports of small glass beads and pendants have been made from sites that date to the mid-third millennium from the Near East. These are amongst the earliest known works of glass making and utilised lapidary techniques in their cutting and grinding in the cold state (Freestone 1991). Glass is not convincingly attested in Ancient Egypt before the late Middle Kingdom and is comparatively rare in the archaeological record before c. 1 550 (the beginning of the New Kingdom with the Eighteenth Dynasty) (Lilyquist & Brill 1993). It has been proposed that the craft of glass making was first introduced full-scale into Egypt by glass makers captured by Thutmose II (1 479 – 1 425 BC) from the state of Mitanni (situated between the Tigris and Euphrates river, it developed into a powerful state some time before 1 500 BC and became one of Egypt’s most powerful enemies), where the technology was readily available, on one of his numerous campaigns. This hypothesis is backed by the tribute lists dating to this period, the Annals of Thutmose II at Karnak, which list glass as one of the materials (Nicholson 1993). By extension, glass was then held in high esteem with great significance of some kind attached to it. This importance was still great enough a century later by the rule of Akhenaten (1 352 – 1 336 BC) to warrant its inclusion in official diplomatic correspondence. These are the famous Amarna Letters, in which the words ehlipakku and mekku are written (Shaw & Nicholson 1995 [5]). These are Hurrian and Akkadian terms respectively, and their importation into the Ancient Egyptian language is a possible indicator as to the eastern origin of the earliest glass.
It is this admittedly hypothetical scenario of an importation of craftsmen from abroad that is believed to account for the distinct absence of any surviving instances of trial stages in the making of glass in Ancient Egypt (Shaw and Nicholson 1995). Instead, glass making emerges as a fully-fledged industry. Accordingly, technologically arduous compositions, such as clear decolorised glass, are known from as early as the reign of Hatshepsut (1 473 – 1 458 BC) and the colourless glass inlays imbedded in the throne of Tutankhamun (1 336 – 1 327 BC).
Apart from its utilisation in amulets, beads and inlays, attempts were made to use glass in more ambitious projects, including that of vessels. The technique of vessel manufacture by means of blowing was only introduced into Egypt during the Roman era. The other means was core-forming: a handling rod would be used around which the craftsman would form and shape a core of mud and sand in the shape of the vessel’s interior (Shaw & Nicholson 1995). The next step would be for the core to be submerged into the viscous molten glass (an alternative method would be for the glass to be trailed over it) and leveled by means of rolling the whole on a flat stone called marver. Pincers would then be used to shape the feet and rims of the vessels. It was usually from here that the process became more complicated. The base colour of the vessel was usually either blue or blue-green. To this colour threads were supplemented so that the end effect was strands of yellow, white, red, etc., decorating the piece. These threads were sometimes pulled with a needle in order to form swag or feather patterns and then they were rolled on the marver to imprint them into the body of the glass that was still soft and therefore impressionable (Nicholson 1993).
The vessel was then placed into an oven where it was allowed to slowly cool. This is a processing termed annealing (Shaw & Nicholson 1995). Annealing permits the gradual release of stresses that had developed within the glass. When the glass had cooled, the core would then be broken up and extracted through the opening of the vessel. There was frequent difficulty in removing the core in its entirety, specifically in the shoulders of the narrow-necked vessels (Lilyquist & Brill 1993). This led to the remnants of the core often adding to the opacity of these pieces, while those that had broader necks often appear more translucent.
Glass could also be molded. In its simplest form, this involved the fashioning of clear glass forms. However, it could also be a more complicated process involving sections of different coloured glass cane being fused together in a mould to make multi-coloured vessels (Shaw & Nicholson 1995). Examples of these would include yellow eyes on a green background, or the conglomerate glass pieces with angular fragments of many colours fused into bowls.
Glass was also worked by means of cold cutting in Ancient Egypt. This process involved the working of lumps of glass, sometimes roughly molded into the desired shape, as though they were pieces of stone and thereafter shaped by means of carving (Shaw & Nicholson 1995). This extremely difficult process, that required enormous amounts of skill and practice, were the means by which some fine pieces (including two headrests of Tutankhamun) were crafted.
The available evidence suggests that in Ancient Egypt glass was hailed, or at least regarded, as an artificial semi-precious stone and, like such stones, sometimes is imitated in painted wood. It has been proposed that it is because of this connection that glass never developed forms of its own in Ancient Egypt but rather copied those traditionally made in stone, faience or other materials (Nicholson 1993). For the Ancient Egyptians of the New Kingdom glass was a costly novelty material, most likely under the control of the royalty and given as presents to the favoured officials. Until comparatively recent times the line of thought was that the production of glass declined after the 21st Dynasty (1 069 – 945 BC) and was not revived on any scale until the 26th dynasty (664 – 525 BC). However, glass making continued on a much reduced scale. Down in the Greek (Ptolemaic) era the center of glass craftsmanship was the famous city of Alexandria with the manufacture of core-formed vessels and, in Roman times, of items of cameo glass that likely included the famous Portland Vase stored in the British Museum.
Glass, because of the extensive palette of colours available for utilising in its manufacture, cannot therefore be interpreted by either its colours or its degree of transparency. Modern scientists classify it based on its atomic composition. The similarity of its atom arrangement to that of molten liquid is the same. This occurs through the strong chemical bond that binds the atoms and the stiffness prevents atomic re-adjustment during the cooling process (Freestone 1991). Therefore, it is the liquid structure of glass that is liable for many of its distinguishing characteristics.
The chemical composition of glass
The primary constituent making up the chemical composition of glass is silica (silicon dioxide), which is the most common component of the earth’s crust and accounts for 50-70% of the weight of ancient glass (Freestone 1991). The silica is extracted from raw materials as freely available as quartz sand, white quartz pebbles and flint. The metallurgical furnaces and pottery kilns utilised in ancient times were not, however, capable of heating crushed quartz pebbles to the temperature required for them to melt. Therefore a flux was introduced and combined with the silica (Freestone 1991). This enabled the lowering of the melting temperature and the resultant manufacturing of glass. It has been estimated that the introduction of 20% flux would lead to the reduction of the melting temperature of quartz by as much as over 700 degrees, from about 1700 degrees centigrade to below 1000 degrees centigrade (Freestone 1991).
Alkalis were utilised in ancient times as flux. These were usually soda (sodium oxide) and potash (potassium oxide). The alkalis were gleaned either from naturally occurring minerals or from the ashes left behind by burnt plant material or wood. Nevertheless, a combination of silica and pure soda/potash would not have resulted in high quality glass (Freestone 1991). A stabiliser was needed which would lessen the solubility of the glass and prevent it corroding within a relatively short timeframe. The ancient stabiliser was more often than not lime (calcium oxide). It is questionable whether the calcium oxide was a deliberate inclusive on the part of the ancient glassmakers or whether its occurrence was accidental, either in conjunction with the silica or with the alkali, and the glass manufacturers were unaware of it as a separate component (Freestone 1991). Lime is chemical closely related to magnesia.
It is noticeable that the chemical compositions of ancient glass are relatively similar to those of the modern era, with the medieval period providing an exception. The compositions are soda-lime-silica glasses, with sodium oxide providing the flux and calcium oxide the stabiliser. Therefore, by the time of the second millennium BC, it appears that a glass formulation with a formula relatively similar to that of modern glass had been obtained and utilised with widespread familiarity.
The major chemical constituents of glass are: silica or sand (SiO2), sodium oxide (Na2O) or potassium oxide (K2O) as a fluxing or alkali agent that reduces the melting temperature of silica, and calcium oxide (CaO) from lime. Impurities within the silica include: alumina (A12O3), copper (Cu), iron (Fe2O3) and magnesium (MgO). It is likely that the fluxing agents cited above also contained traces of chlorite, phosphoric oxide and sulphate (Saitowitz 1996).
The predominant types of early glasses were soda-lime-silica and potash-lime-silica glasses. The raw materials utilised by the ancient glassmakers would first have been put through cleansing processes before they were put to use. These processes would have most probably included forms of screening, washing and burning for extraneous coarse particles, organic matter and other impurities to be expunged (Saitowitz 1996). This would have been particularly true of sand. As the ancients lacked the modern technological methods and available synthetic materials, the end result was a product which only at times was not quite as refined as those that have been obtained in the modern era. In particular, unsightly spots and other visual faults were caused by the zircon, ilmenite and rutile heavy minerals not having melted in the glassy matrix (Saitowitz 1996).
Of the differing raw materials required for glass making, sand is the most available and the least expensive. There is no fixed amount of sand that is needed during preparation, as the relatively wide limits do not lend themselves to lessening the quality of the glass produced (Saitowitz 1996). The exact origin locations of the sands that were used in the various parts of the ancient world are currently unknown, due to the lack of the necessary analytical studies and to the lack of mention in the ancient records. If it were not for the mentions of Pliny and Strabo, almost nothing would exist from the ancient accounts. Pliny singles out the sands of the Belus River on the Palestinian coast (stretching from Acre to Tyre) and Strabo the sands to north-west of the ancient Roman harbours of Pozzuali and Naples as raw material source places (Tatton-Brown & Andrews 1991).
The alkali flux soda (Na2O, NaHCO3, and Na2CO3) is one of the prominent ingredients of glass. Some soda glasses have been found to contain as much as 23% Na2O, but this content makes them vulnerable to deterioration through weathering. This impure sodium carbonate and bicarbonate form of alkali can be found in Egypt at Wadi Natrun and El Kab (Saitowitz 1996). The lakes at Wadi Natrun overlie a complex series of geological formations. Somewhat sweet water can be found in a couple of the lakes, with others containing predominantly sodium sulphate, carbonate or chloride. Lakes containing sodium carbonate would have been a natural and readily available source for glass making. Other sources of sodium carbonate were available, however: evaporates from dried seas, soils which leached salt deposits, and the salts given off by specific plants when subjected to burning (Saitowitz 1996). The Chinane (known locally in Syria as the Keli) was incredibly rich in sodium carbonate in its ash remains.
Potassium oxide (K2O) can replace sodium oxide as the flux in glass, resulting in a greater level of brilliance as well as a superior colour. The resultant glasses posses a higher melting point, and is solid and more enduring. The necessary potassium compounds are extracted from plant and wood ashes. The New Kingdoms sites of Thebes and Tel el-Amarna show significant traces of potassium oxide, in contrast to the virtual lack in glasses from Alexandria. This supports the above suggestion from the soda flux that more than one source of alkali was available to the Ancient Egyptians and utilised by them.
Calcium (lime – CaO) acts as a stabiliser to glass, allowing it to harden more rapidly during the cooling process. By making the glass more durable it has a side effect: it makes the glass more resistant to water penetration. Much limestone is derived from a dolomitic variety and contains a variable amount of MgO with the CaO. These are often present in equal ratios. As MgO is a common constituent of Egyptian glasses, it has been hypothesised that the composition of the sand may be responsible for its presence in the glass. Most of the sand of Egypt’s northern coast contains calcium carbonate as an impurity, a factor that could explain a variance occurring naturally, rather than by the intentional addition of lime to the batch. Calcium derivatives commonly occur in nature as calcium oxide or lime. Calcium carbonate (CaCO3), for example, is present in sea shells, limestone and chalk. Low lead-soda-lime-silica compositions contain up to 8% CaO while lead glasses usually consist of 2.5% (Saitowitz 1996).
From the beginning of the Roman period, starting around the seventh century BC in Italy, a new second kind of glass began spreading throughout the Mediterranean world. This glass has been termed “low-magnesia glass”, after its percentage of both the magnesia and potassium oxide components is less than 1% (Freestone 1991). The higher counts of magnesia and potassium oxide in the glasses from the previous millennia were the result of the utilisation in the manufacturing process of plant ash. Plant ash is not composed of pure soda. Roman glass-makers, however, achieved a result of low impurities through the application of high-quality soda or natron. The site of Wadi Natrun, an oasis that featured natural salt lakes, is located in Egypt’s Western Desert. From here natron was distributed through the Mediterranean world. Indeed, it become the main depository for the Mediterranean, and thereby comprehensive and extensive trade networks are implied (Freestone 1991).
Ancient Egyptian New Kingdom glass
The dark amethyst-coloured glass of the Eighteenth (1 550 – 1069 BC) and Twentieth dynasties (1 186 – 1069 BC) owe their colour to a manganese compound, of which 0.5 – 0.7% has been calculated as oxide (Lucas & Harris 1962 [7]). It is interesting to note that white glass of ordinary quality containing manganese compounds becomes coloured if it is exposed to strong sunlight for a certain period of time. The resultant colour varies from a light amethyst tint to a deep purple colour, and it is a matter of common observation in Egypt even today to find in the desert, in the vacinity of towns, pieces of were white glass coloured in this way. This colouration is the result of the manganese compounds within the glass having undergone some chemical change, which is apparently brought about by sunlight and is not caused either by way of heat or radio-activity, although the latter produces a similar colouration as well (Lucas & Harris 1962). However, the conclusion cannot be reached that the colour of ancient amethyst glass has been caused by exposure or that it is other than original.
The colouring of the Ancient Egyptian black glass was caused by three compounds varying in proportion to each other and thereby in visual effect: copper and manganese, and iron (Lucas & Harris 1962). Although black glass was certainly manufactured in Egypt at a late date, the early black glass (which, amongst others, was used to manufacture beads) was due to the use of impure materials that contained, for instance, a large proportion of iron compounds (Lucas & Harris 1962).
The blue glasses of the Ancient Egyptians were primarily three shades: dark blues, which imitated lapis lazuli with often a great deal of success, light blues that imitated turquoise, and greenish blue that imitated both felspar and turquoise (Lucas & Harris 1962). In modern Egypt, a cobalt compound is used for colouring blue glass. Yet, cobalt only produces a dark blue colour. Consequently, the turquoise blue and the greenish-blue of some of the Ancient Egyptian glass cannot be the result of its use.
Many of the blue glass specimens from the Eighteenth and Twentieth dynasties owe their colouring to a copper compound. There is one specimen, though, from the tomb of Tutankhamun that was coloured by a cobalt compound (Lucas & Harris 1962). On rare occasions it has been found that the colouring was caused by an iron compound. Pieces have also been found from the eighth to the sixth century BC which contain both copper and cobalt. In the majority of the blue glasses that have been excavated and examined, the colour, whether the result of copper or cobalt, was modified by the presence of manganese (Lucas & Harris 1962).
The presence of cobalt in Ancient Egyptian glass at an early a date as the eighteenth Dynasty is of considerable importance. Cobalt compounds do not appear in Egypt except as traces in other minerals (Lucas & Harris 1962). Their presence in the glass points towards the Ancient Egyptian glassmakers from that era being in contact with glassmakers elsewhere who were utilising this material.
The green glass derives its colour either from compounds of copper or of iron. The colouration of the modern green bottle-glass is, for example, produced by the latter method. By contrast, the Ancient Egyptians of the eighteenth and Twentieth dynasties utilised a copper compound (Lucas & Harris 1962).
The red oxide of copper causes the colour of the Ancient Egyptian Eighteenth Dynasty red glass, as is evident from the green coating that forms on the surface when the glass decays (Lucas & Harris 1962).
The Nile limestone bluffs stretch from Luxor to just beneath Cairo. The sands bordering these bluffs therefore contain a high calcium (lime) content, which would have affected different glass-making centers situated in this region of the Nile, e.g. Fustat and Tel el-Amarna (Saitowitz 1996). The techniques for glazing of such stones as quartz and steatite, and the production of faience, had been known to the Ancient Egyptians since Predynastic times (c. 5 500 – 3 100 BC). Flinders Petrie discovered glass waste during his excavations at Tel el-Amarna, which was the capital of Ancient Egypt during the reign of the Pharaoh Akhenaten (Shaw & Nicholson 1995). This, one of the earliest examples of a substantial glassmaking industry, consisted of plain open-hearth furnaces together with small crucibles. Newer excavations during the course of the early 1990s have produced new evidence based primarily on the detailed study of kilns. These studies increasingly consider it likely that glass making was carried on alongside faience production and possibly other pyrotechnical crafts (Shaw & Nicholson 1995). Apart from El-Amarna, there are other glass working sites at El-Lisht and Malkata.
The glassy matrix
The site of Mendes in the Nile Delta was occupied in ancient times right from Predynastic times (from the fourth millennium BC onwards) down into the occupation first by the Greeks and then by the Romans (332 BC – 395 AD). The span of Mendes currently measures 1.5 square km, and its size has been reduced considerably through the devastating encroachment of agricultural fields. Mendes is also known in archaeological circles as Tell er-Ruba’a. Outside the remains of Mendes’ eastern enclosure wall is the related site of Kom el-Adhem at a distance of about 100m. The literal translation of Kom el-Adhem is the “hill of bones”, and it lives up to its name for it is here that animal teeth and bone are to be seen trapped within a glassy matrix in large quantities. Also relatively nearby Kom el-Adhem is the site of Thmuis. The occupational, religious and social connections and dynamics between these three sites are not completely certain. It is hypothesised, though, that Kom el-Adhem served as a harbour in its early history and later a religious function in the guise of a mortuary complex during the Graeco-Roman period. The latter assumption is based on burials excavated at the site dating to this period.
The mass aggregate of teeth and bones are found approximately 50 to 100m downslope of the burials, with sections exposed through the effects of weather erosion. One exposed area covers about 40m in width, with some blocks averaging between 0.5m in width and 1m in length, and it was from this aggregate that Magee, Wayman and Lovell (1996) extracted samples for testing its chemical and microstructural composition to determine both the processes of its formation and its resulting origins.
Volcanic activity is one common natural phenomenon that produces glassy residues as a by-product. However, on archaeological sites it has been more generally from metallurgical procedures as is known as slag (Magee et al. 1996). Slag is essentially the extraneous material that has been extracted from an ore product during the smelting process. Yet, this is not the only role played by industrial slag. The potential exists during the process of smelting of an interaction between the surrounding environment and the molten metal being attended to; slag operates as a protective measure. Slag in the archaeological literature is also used in reference to residues from glass-making, brick and tile production, lime burning, pottery manufacture, cremation, furnace and hearth vitrified fuel ash, vegetable ash, cinder ash from cow dung (e.g. Southern India) and destruction slags from burnt vitrified forts. In archaeological terms, therefore, “slag” is used to designate a glassy mass either partly or fully liquefied that was caused by silica or silicates interacting with fluxing compounds at high temperatures (Magee et al. 1996).
In applying this terminology to the glassy matrix at Kom el-Adhem Magee, Wayman and Lovell (1996) note that the slag is on a flat surface of sand and positioned such that the likelihood of it having slid down from further up the mound slope is remote. A glassy crust covers the sediments that surround the slag. The sand at the point of intersection with the glassy crust was reddened. This indicates that the formation of the slag in situ most probably coincided with the burning of the sand in the immediate vacinity (Magee et al. 1996).
The first 1m of sand beneath the surrounding surface is barren. Then, however, there is a strata containing animal bones teeth and horns from overridingly sheep and goats, with some avian also; no remains identifiable as large animals, e.g. bovids and equids, are present. These faunal remains are fragmentary and therefore observation of the processes of articulation is minimal. Directly underneath the faunal remains are the remnants of a mudbrick structure in the form of a layer of deteriorated mudbrick, making the identification of architectural features hazardous (Magee et al. 1996). It is likely that this structure was originally located uphill to the northwest and collapsed downslope. These mudbrick remains primarily contained also small quantities of goat and sheep remains. The topographic stratas of the slag and the surrounding sand follow that of the mound: northwest to southeast.
Magee, Wayman and Lovell (1996) used stereobinocular optical microscopy, combined with unaided sight examination, to determine the physical characteristics of the slag that dominated. The samples were embedded in epoxy resin, ground with silicon carbide abrasive papers to 600 grit, and polished with 6 um diamond abrasive slurry and 0.05 um aluminum oxide slurry. These polished samples were examined with an incident light optical microscope and a Hitachi S-2700 scanning electron microscope (SEM) equipped with a Link eXL energy dispersive X-ray microanalysis (EDA) system. The aim was to identify and individually analyse its microstructural constituents. Utilising standard petrographic techniques, a thin section of the slag was examined after preparation. Slag samples were ground into powder for x-ray diffraction analysis and the matrix and bone particles were separated manually so that both constituents could be analysed separately (Magee et al. 1996).
The macroscopic examinations confirmed that the aggregate was a glassy matrix containing bone and teeth. The matrix is mostly black and visicular, ranging from 1 – 6mm in diameter with their interior comprised of a reddish tint (Magee et al. 1996). The bone colour fluctuates between yellow and yellow-red, which is within the normal range of colour. Bones that have been exposed to high temperatures show signs of cracking and checking, but these are not evident on the bones from the glassy matrix. However, the point of intersection between bone and the matrix reveals the bone displays colours ranging from blue to purple. A clear, polished substance coats the tips of bones or the bone fragments protruding from the matrix. Quartz grains are, together with other mineral grains, are implanted within the matrix (Magee et al. 1996).
The results of the SEM examination revealed the samples’ microstructure to consist of a complex phase mixture (Magee et al. 1996).
The identification of the differing bright, grey and dark matrix phases was done by SEM-EDA analysis. The study involved utilizing semi-quantitative elemental analyses, converted to oxide percent and normalised. Analyses of this type are commonly used in the material sciences for phase checking. When they are checked regularly against analysed standards, as happened in this case, they are suitable for general comparison with the quantitative analyses of other materials reported in the scientific literature (Magee et al. 1996).
Energy dispersive microanalysis was conducted on three areas of the sample matrix. The results demonstrate that the matrix is a heterogeneous silicate that possesses aluminum, iron and potassium. Smaller traces of calcium, magnesium, sodium and titanium are also present (Magee et al. 1996). The microstructural elements, in their form as diverse particles composing the silicate matrix, were bone fragments, iron oxide, and silicates. The bone fragments were identified through their calcium and phosphorus components. To the left of the trapezoidal bone fragment is a tear drop-shaped constituent identified as a silica quartz particle. The lower left displays a circular dark feature that is a vesicle packed with the epoxy mounting material (Magee et al. 1996). The small, bright and angular grains are probably an iron-rich phase, tentatively identified as iron oxide, and which contains small traces of magnesium and titanium. The small and wispy silicate particles have the same chemical components as the matrix. Their appearance in the matrix points towards the possibility of small crystals having formed in the glassy matrix. The cooling of the matrix during its formation process could have caused this, which caused devitrification. The tiny spherical particles are rich in calcium and phosphorus. Accurate determination of their composition is precluded through the sub-micron size of these particles being smaller than the volume analysed by the SEM-EDA technique. Their measured compositions are, therefore, those of particles together with a notable but indeterminate contribution from the surrounding matrix. Their compositions strongly point toward derivation from bone material, possibly as immiscible droplets of a phosphate-rich liquid (Magee et al. 1996).
The x-ray diffraction results obtained from the matrix material were consistent with a large portion of the sample being amorphous. Also present were diffraction peaks from many crystalline phases. These were identified as quartz (SiO2), the iron oxides magnetite (Fe3O4) and hematite (Fe2O3), and a crystalline silicate of the feldspar type that most closely resemble anorthite. This …