Amber

This is about the material called amber. For other things called amber, see Amber (disambiguation).

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Amber pendants. The oval pendant is 52 by 32 mm (2 by 1.3 inches).

Amber is a fossil resin much used for the manufacture of ornamental objects. Although not mineralized it is sometimes considered and used as a gemstone.

History

The name comes from the Arabic anbar, probably through the Spanish, but this word referred originally to ambergris, which is an animal substance quite distinct from yellow amber. True amber has sometimes been called karabe, a word of oriental derivation signifying "that which attracts straw", in allusion to the power which amber possesses of acquiring an electric charge by friction. This property, first recorded by Thales of Miletus, suggested the word "electricity", from the Greek, elektron, a name applied, however, not only to amber but also to an alloy of gold and silver. By Latin writers amber is variously called electrum, sucinum (succinum), and glaesum or glesum. The Old Hebrew hashmal seems to have meant amber, although Modern Hebrew uses Arabic-inspired i'nbar. The German word is Bernstein.

Composition

Amber is heterogeneous in composition, but consists of several resinous bodies more or less soluble in alcohol, ether and chloroform, associated with an insoluble bituminous substance. The average composition of amber leads to the general formula C₁₀H₁₆O. Heated rather below 300°C, amber suffers decomposition, yielding an "oil of amber", and leaving a black residue which is known as "amber colophony", or "amber pitch"; when dissolved in oil of turpentine or in linseed oil this forms "amber varnish" or "amber lac".

True amber yields on dry distillation succinic acid, the proportion varying from about 3 to 8%, and being greatest in the pale opaque or bony varieties. The aromatic and irritating fumes emitted by burning amber are mainly due to this acid. True Baltic amber is distinguished by its yield of succinic acid, for many of the other fossil resins which are often termed amber contain either none of it, or only a very small proportion; hence the name succinite proposed by Professor J. D. Dana, and now commonly used in scientific writings as a specific term for the real Prussian amber. Succinite has a hardness between 2 and 3, which is rather greater than that of many other fossil resins. Its specific gravity varies from 1.05 to 1.10.

The Baltic amber or succinite is found as irregular nodules in a marine glauconitic sand, known as blue earth, occurring in the Lower Oligocene strata of Samland in East Prussia, where it is now systematically mined. It appears, however, to have been partly derived from yet earlier Tertiary deposits (Eocene); and it occurs also as a derivative mineral in later formations, such as the drift. Relics of an abundant flora occur in association with the amber, suggesting relations with the flora of Eastern Asia and the southern part of North America. H. R. Goppert named the common amber-yielding pine of the Baltic forests Pinites succiniter, but as the wood, according to some authorities, does not seem to differ from that of the existing genus it has been also called Pinius succinifera. It is improbable, however, that the production of amber was limited to a single species; and indeed a large number of conifers belonging to different genera are represented in the amber-flora.

An insect trapped in amber. The amber piece is 10 mm (0.4 inches) long. In the enlarged picture, the insect's antennae are easily seen.

The resin contains, in addition to the beautifully preserved plant-structures, numerous remains of insects, spiders, annelids, crustaceans and other small organisms which became enveloped while the exudation was fluid. In most cases the organic structure has disappeared, leaving only a cavity, with perhaps a trace of chitin. Even hair and feathers have occasionally been represented among the enclosures. Fragments of wood not infrequently occur, with the tissues well-preserved by impregnation with the resin; while leaves, flowers and fruits are occasionally found in marvellous perfection. Sometimes the amber retains the form of drops and stalactites, just as it exuded from the ducts and receptacles of the injured trees. The abnormal development of resin has been called succinosis. Impurities are often present, especially when the resin dropped on to the ground, so that the material may be useless except for varnish-making, whence the impure amber is called firniss. Enclosures of pyrites may give a bluish colour to amber. The so-called black amber is only a kind of jet. Bony amber owes its cloudy opacity to minute bubbles in the interior of the resin.

Locations and Ultilization

Although amber is found along the shores of a large part of the Baltic Sea and the North Sea, the great amber-producing country is the promontory of Samland. Pieces of amber torn from the sea-floor are cast up by the waves, and collected at ebb-tide. Sometimes the searchers wade into the sea, furnished with nets at the end of long poles, by means of which they drag in the sea-weed containing entangled masses of amber; or they dredge from boats in shallow water and rake up amber from between the boulders. Divers have been employed to collect amber from the deeper waters. Systematic dredging on a large scale was at one time carried on in the Kurisches Haff by Messrs Stantien and Becker, the great amber merchants of Königsberg. At the present time extensive mining operations are conducted in quest of amber. The pit amber was formerly dug in open works, but is now also worked by underground galleries. The nodules from the blue earth have to be freed from matrix and divested of their opaque crust, which can be done in revolving barrels containing sand and water. The sea-worn amber has lost its crust, but has often acquired a dull rough surface by rolling in sand.

Amber is extensively used for beads and other trivial ornaments, and for cigar-holders and the mouth-pieces of pipes. It is regarded by the Turks as specially valuable, inasmuch as it is said to be incapable of transmitting infection as the pipe passes from mouth to mouth. The variety most valued in the East is the pale straw-coloured, slightly cloudy amber. Some of the best qualities are sent to Vienna for the manufacture of smoking appliances. In working amber, it is turned on the lathe and polished with whitening and water or with rotten stone and oil, the final lustre being given by friction with flannel. During the working much electricity is developed.

When gradually heated in an oil-bath amber becomes soft and flexible. Two pieces of amber may be united by smearing the surfaces with linseed oil, heating them, and then pressing them together while hot. Cloudy amber may be clarified in an oil-bath, as the oil fills the numerous pores to which the turbidity is due. Small fragments, formerly thrown away or used only for varnish, are now utilized on a large scale in the formation of "ambroid" or "pressed amber". The pieces are carefully heated with exclusion of air and then compressed into a uniform mass by intense hydraulic pressure; the softened amber being forced through holes in a metal plate. The product is extensively used for the production of cheap jewellery and articles for smoking. This pressed amber yields brilliant interference colours in polarized light. Amber has often been imitated by other resins like copal and kauri, as well as by celluloid and even glass. True amber is sometimes coloured artificially.

Amber was much valued as an ornamental material in very early times. It has been found in Mycenaean tombs; it is known from lake-dwellings in Switzerland, and it occurs with neolithic remains in Denmark, whilst in England it is found with interments of the bronze age. A remarkably fine cup turned in amber from a bronze-age barrow at Hove is now in the Brighton Museum. Beads of amber occur with Anglo-Saxon relics in the south of England; and up to a comparatively recent period the material was valued as an amulet. It is still believed to possess a certain medicinal virtue.

Rolled pieces of amber, usually small but occasionally of very large size, may be picked up on the east coast of England, having probably been washed up from deposits under the North Sea. Cromer is the best-known locality, but it occurs also on other parts of the Norfolk coast, as well as at Great Yarmouth, Southwold, Aldeburgh and Felixstowe in Suffolk, and as far south as Walton-on-the-Naze in Essex, whilst northwards it is not unknown in Yorkshire. On the other side of the North Sea, amber is found at various localities on the coast of the Netherlands and Denmark. On the shores of the Baltic it occurs not only on the Prussian and Pomeranian coast but in the south of Sweden, in Bornholm and other islands, and in southern Finland. Amber has indeed a very wide distribution, extending over a large part of northern Europe and occurring as far east as the Urals. Some of the amber districts of the Baltic and North Sea were known in prehistoric times, and led to early trade with the south of Europe. Amber was carried to Olbia on the Black Sea, Massilia (today Marseille) on the Mediterranean, and Hatria at the head of the Adriatic; and from these centres it was distributed over the Hellenic world.

Amber and certain similar substances are found to a limited extent at several localities in the United States, as in the green-sand of New Jersey, but they have little or no economic value. A fluorescent amber is said, however, to occur in some abundance in Southern Mexico. Amber is recorded also from the Dominican Republic.

Varieties

Whilst succinite is the common variety of European amber, the following varieties also occur: --

• Gedanite, or brittle amber, closely resembling succinite, but much more brittle, not quite so hard, with a lower melting- point and containing no succinic acid. It is often covered with a white powder easily removed by wiping. The name comes from Gedanum, the Latin name of Danzig at the Baltic Sea.

• Stantienite, a brittle, deep brownish-black resin, destitute of succinic acid.

• Beckerite, a rare amber in earthy-brown nodules, almost opaque, said to be related in properties to gutta-percha.

• Glessite, a nearly opaque brown resin, with numerous microscopic cavities and dusty enclosures, named from glesum, an old name for amber.

• Krantzite, a soft amber-like resin, found in the lignites of Saxony.

• Allingite, a fossil resin allied to succinite, from Switzerland.

• Roumanite, or Romanian amber, a dark reddish resin, occurring with lignite in Tertiary deposits. The nodules are penetrated by cracks, but the material can be worked on the lathe. Sulphur is present to the extent of more than 1%, whence the smell of sulphuretted hydrogen when the resin is heated. According to Gheorghe Murgoci the Romanian amber is true succinite.

• Simetite, or Sicilian amber, takes its name from the river Simeto or Giaretta. It occurs in Miocene deposits and is also found washed up by the sea near Catania. This beautiful material presents a great diversity of tints, but a rich hyacinth red is common. It is remarkable for its fluorescence, which in the opinion of some authorities adds to its beauty. Amber is also found in many localities in Emilia, especially near the sulphur-mines of Cesena. It has been conjectured that the ancient Etruscan ornaments in amber were wrought in the Italian material, but it seems that amber from the Baltic reached the Etruscans at Hatria. It has even been supposed that amber passed from Sicily to northern Europe in early times -- a supposition said to receive some support from the fact that much of the amber dug up in Denmark is red; but it must not be forgotten that reddish amber is found also on the Baltic, though not being fashionable it is used rather for varnish-making than for ornaments. Moreover, yellow amber after long burial is apt to acquire a reddish colour. The amber of Sicily seems not to have been recognized in ancient times, for it is not mentioned by local authorities like Diodorus Siculus.

• Burmite is the name under which the Burmese amber is now described. Until the British occupation of Burma but little was known as to its occurrence, though it had been worked for centuries and was highly valued by the natives and by the Chinese. It is found in fiat rolled pieces, irregularly distributed through a blue clay probably of Miocene age. It occurs in the Hukawng valley, in the Nangotaimaw hills, where it is irregularly worked in shallow pits. The mines were visited some years ago by Dr Fritz Noetling, and the mineral has been described by Dr Otto Helm. The Burmese amber is yellow or reddish, some being of ruby tint, and like the Sicilian amber it is fluorescent. Burmite and simetite agree also in being destitute of succinic acid. Most of the Burmese amber is worked at Mandalay into rosary-beads and ear-cylinders.

Many other fossil resins more or less allied to amber have been described. Schraufite is a reddish resin from the Carpathian sandstone, and it occurs with jet in the Cretaceous rocks of the Lebanon; ambrite is a resin found in many of the coals of New Zealand; retinite occurs in the lignite of Bovey Tracey in Devonshire and elsewhere; whilst copaline has been found in the London clay of Highgate in North London. Chemawinite or cedarite is an amber-like resin from the Saskatchewan river in Canada.

See also: List of minerals