Pendants made of amber. The oval pendant is 52 by 32 mm (2 by 1 14 in).
An ant inside Baltic amber
The Amber Room in the Catherine Palace, Saint Petersburg was reconstructed using new amber from Kaliningrad
Unpolished amber stones
Extracting Baltic amber from Holocene deposits, Gdansk, Poland

Amber is fossilized tree resin, which has been appreciated for its color and natural beauty since Neolithic times.[1] Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects.[2] Amber is used in jewelry. It has also been used as a healing agent in folk medicine.

There are five classes of amber, defined on the basis of their chemical constituents. Because it originates as a soft, sticky tree resin, amber sometimes contains animal and plant material as inclusions.[3] Amber occurring in coal seams is also called resinite, and the term ambrite is applied to that found specifically within New Zealand coal seams.[4]

Etymology

The English word amber derives from Arabic ʿanbar عنبر[5] (cognate with Middle Persian ambar[6]) via Middle Latin ambar and Middle French ambre. The word was adopted in Middle English in the 14th century as referring to what is now known as ambergris (ambre gris or "grey amber"), a solid waxy substance derived from the sperm whale. In the Romance languages, the sense of the word had come to be extended to Baltic amber (fossil resin) from as early as the late 13th century. At first called white or yellow amber (ambre jaune), this meaning was adopted in English by the early 15th century. As the use of ambergris waned, this became the main sense of the word.[5]

The two substances ("yellow amber" and "grey amber") conceivably became associated or confused because they both were found washed up on beaches. Ambergris is less dense than water and floats, whereas amber is too dense to float, though less dense than stone.[7]

The classical names for amber, Latin electrum and Ancient Greek ἤλεκτρον (ēlektron), are connected to a term ἠλέκτωρ (ēlektōr) meaning "beaming Sun".[8][9] According to myth, when Phaëton son of Helios (the Sun) was killed, his mourning sisters became poplar trees, and their tears became elektron, amber.[10] The word elektron gave rise to the words electric, electricity, and their relatives because of amber's ability to bear a charge of static electricity.[11]

History

Theophrastus discussed amber in the 4th century BC, as did Pytheas (c. 330 BC), whose work "On the Ocean" is lost, but was referenced by Pliny the Elder (23 to 79 AD), according to whose The Natural History (in what is also the earliest known mention of the name Germania):[12]

Pytheas says that the Gutones, a people of Germany, inhabit the shores of an estuary of the Ocean called Mentonomon, their territory extending a distance of six thousand stadia; that, at one day's sail from this territory, is the Isle of Abalus, upon the shores of which, amber is thrown up by the waves in spring, it being an excretion of the sea in a concrete form; as, also, that the inhabitants use this amber by way of fuel, and sell it to their neighbors, the Teutones.

Fishing for amber on the coast of Baltic Sea. Winter storms throw out amber nuggets. Close to Gdansk, Poland.

Earlier[13] Pliny says that Pytheas refers to a large island - three days' sail from the Scythian coast and called Balcia by Xenophon of Lampsacus (author of a fanciful travel book in Greek) - as Basilia - a name generally equated with Abalus. Given the presence of amber, the island could have been Heligoland, Zealand, the shores of Bay of Gdansk, the Sambia Peninsula or the Curonian Lagoon, which were historically the richest sources of amber in northern Europe.[citation needed] It is assumed[by whom?] that there were well-established trade routes for amber connecting the Baltic with the Mediterranean (known as the "Amber Road"). Pliny states explicitly that the Germans exported amber to Pannonia, from where the Veneti distributed it onwards.

The ancient Italic peoples of southern Italy used to work amber; the National Archaeological Museum of Siritide (Museo Archeologico Nazionale della Siritide) at Policoro in the province of Matera (Basilicata) displays important surviving examples. Amber used in antiquity as at Mycenae and in the prehistory of the Mediterranean comes from deposits of Sicily.[citation needed]

Wood resin, the source of amber

Pliny also cites the opinion of Nicias (c. 470–413 BC), according to whom amber

is a liquid produced by the rays of the sun; and that these rays, at the moment of the sun's setting, striking with the greatest force upon the surface of the soil, leave upon it an unctuous sweat, which is carried off by the tides of the Ocean, and thrown up upon the shores of Germany.

Besides the fanciful explanations according to which amber is "produced by the Sun", Pliny cites opinions that are well aware of its origin in tree resin, citing the native Latin name of succinum (sūcinum, from sucus "juice").[14] In Book 37, section XI of Natural History, Pliny wrote:

Amber is produced from a marrow discharged by trees belonging to the pine genus, like gum from the cherry, and resin from the ordinary pine. It is a liquid at first, which issues forth in considerable quantities, and is gradually hardened [...] Our forefathers, too, were of opinion that it is the juice of a tree, and for this reason gave it the name of "succinum" and one great proof that it is the produce of a tree of the pine genus, is the fact that it emits a pine-like smell when rubbed, and that it burns, when ignited, with the odour and appearance of torch-pine wood.[15]

He also states that amber is also found in Egypt and in India, and he even refers to the electrostatic properties of amber, by saying that "in Syria the women make the whorls of their spindles of this substance, and give it the name of harpax [from ἁρπάζω, "to drag"] from the circumstance that it attracts leaves towards it, chaff, and the light fringe of tissues".

Pliny says that the German name of amber was glæsum, "for which reason the Romans, when Germanicus Caesar commanded the fleet in those parts, gave to one of these islands the name of Glæsaria, which by the barbarians was known as Austeravia". This is confirmed by the recorded Old High German word glas and by the Old English word glær for "amber" (compare glass). In Middle Low German, amber was known as berne-, barn-, börnstēn (with etymological roots related to "burn" and to "stone"[16]). The Low German term became dominant also in High German by the 18th century, thus modern German Bernstein besides Dutch barnsteen.

In the Baltic languages, the Lithuanian term for amber is gintaras and the Latvian dzintars. These words, and the Slavic jantar[17] and Hungarian gyanta ('resin'), are thought[by whom?] to originate from Phoenician jainitar ("sea-resin").[citation needed]

Early in the nineteenth century, the first reports of amber found in North America came from discoveries in New Jersey along Crosswicks Creek near Trenton, at Camden, and near Woodbury.[2]

Composition and formation

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. Amber is a macromolecule by free radical polymerization of several precursors in the labdane family, e.g. communic acid, cummunol, and biformene.[18][19] These labdanes are diterpenes (C20H32) and trienes, equipping the organic skeleton with three alkene groups for polymerization. As amber matures over the years, more polymerization takes place as well as isomerization reactions, crosslinking and cyclization.

Heated above 200 °C (392 °F), amber decomposes, yielding an oil of amber, and leaves 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".[18]

Formation

Molecular polymerization, resulting from high pressures and temperatures produced by overlying sediment, transforms the resin first into copal. Sustained heat and pressure drives off terpenes and results in the formation of amber.[20]

For this to happen, the resin must be resistant to decay. Many trees produce resin, but in the majority of cases this deposit is broken down by physical and biological processes. Exposure to sunlight, rain, microorganisms (such as bacteria and fungi), and extreme temperatures tends to disintegrate the resin. For the resin to survive long enough to become amber, it must be resistant to such forces or be produced under conditions that exclude them.[21]

Botanical origin

Amber from Bitterfeld

Fossil resins from Europe fall into two categories, the famous Baltic ambers and another that resembles the Agathis group. Fossil resins from the Americas and Africa are closely related to the modern genus Hymenaea,[22] while Baltic ambers are thought to be fossil resins from family Sciadopityaceae plants that once lived in north Europe.[23]

Physical attributes

Most amber has a hardness between 2.0 and 2.5 on the Mohs scale, a refractive index of 1.5–1.6, a specific gravity between 1.06 and 1.10, and a melting point of 250–300 °C.[24]

Inclusions

Baltic amber with inclusions

The abnormal development of resin in living trees (succinosis) can result in the formation of amber.[25] Impurities are quite often present, especially when the resin dropped onto the ground, so the material may be useless except for varnish-making. Such impure amber is called firniss.

Such inclusion of other substances can cause amber to have an unexpected color. Pyrites may give a bluish color. Bony amber owes its cloudy opacity to numerous tiny bubbles inside the resin.[26] However, so-called black amber is really only a kind of jet.

In darkly clouded and even opaque amber, inclusions can be imaged using high-energy, high-contrast, high-resolution X-rays.[27]

Extraction and processing

Distribution and mining

Open cast amber mine "Primorskoje" in Jantarny, Kaliningrad Oblast, Russia

Amber is globally distributed, mainly in rocks of Cretaceous age or younger. Historically, the coast west of Königsberg in Prussia was the world's leading source of amber. The first mentions of amber deposits here date back to the 12th century.[28] About 90% of the world's extractable amber is still located in that area, which became the Kaliningrad Oblast of Russia in 1946.[29]

Pieces of amber torn from the seafloor are cast up by the waves and collected by hand, dredging, or diving. Elsewhere, amber is mined, both in open works and underground galleries. Then nodules of blue earth have to be removed and an opaque crust must be cleaned off, which can be done in revolving barrels containing sand and water. Erosion removes this crust from sea-worn amber.[26]

Caribbean amber, especially Dominican blue amber, is mined through bell pitting, which is dangerous due to the risk of tunnel collapse.[30]

Treatment

The Vienna amber factories, which use pale amber to manufacture pipes and other smoking tools, turn it on a lathe and polish it with whitening and water or with rotten stone and oil. The final luster is given by friction with flannel.[26]

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 used on a large scale in the formation of "ambroid" or "pressed amber".[26] 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 jewelry and articles for smoking. This pressed amber yields brilliant interference colors in polarized light.

Amber has often been imitated by other resins like copal and kauri gum, as well as by celluloid and even glass. Baltic amber is sometimes colored artificially, but also called "true amber".[26]

Appearance

Unique colors of Baltic amber. Polished stones.

Amber occurs in a range of different colors. As well as the usual yellow-orange-brown that is associated with the color "amber", amber itself can range from a whitish color through a pale lemon yellow, to brown and almost black. Other uncommon colors include red amber (sometimes known as "cherry amber"), green amber, and even blue amber, which is rare and highly sought after.[31]

Yellow amber is a hard fossil resin from evergreen trees, and despite the name it can be translucent, yellow, orange, or brown colored. Known to the Iranians by the Pahlavi compound word kah-ruba (from kah "straw" plus rubay "attract, snatch", referring to its electrical properties), which entered Arabic as kahraba' or kahraba (which later became the Arabic word for electricity, كهرباء kahrabā'), it too was called amber in Europe (Old French and Middle English ambre). Found along the southern shore of the Baltic Sea, yellow amber reached the Middle East and western Europe via trade. Its coastal acquisition may have been one reason yellow amber came to be designated by the same term as ambergris. Moreover, like ambergris, the resin could be burned as an incense. The resin's most popular use was, however, for ornamentation—easily cut and polished, it could be transformed into beautiful jewelry. Much of the most highly prized amber is transparent, in contrast to the very common cloudy amber and opaque amber. Opaque amber contains numerous minute bubbles. This kind of amber is known as "bony amber".[32]

Blue amber from Dominican Republic

Although all Dominican amber is fluorescent, the rarest Dominican amber is blue amber. It turns blue in natural sunlight and any other partially or wholly ultraviolet light source. In long-wave UV light it has a very strong reflection, almost white. Only about 100 kg (220 lb) is found per year, which makes it valuable and expensive.[33]

Sometimes amber retains the form of drops and stalactites, just as it exuded from the ducts and receptacles of the injured trees.[26] It is thought that, in addition to exuding onto the surface of the tree, amber resin also originally flowed into hollow cavities or cracks within trees, thereby leading to the development of large lumps of amber of irregular form.

Classification

Amber can be classified into several forms. Most fundamentally, there are two types of plant resin with the potential for fossilization. Terpenoids, produced by conifers and angiosperms, consist of ring structures formed of isoprene (C5H8) units.[1] Phenolic resins are today only produced by angiosperms, and tend to serve functional uses. The extinct medullosans produced a third type of resin, which is often found as amber within their veins.[1] The composition of resins is highly variable; each species produces a unique blend of chemicals which can be identified by the use of pyrolysisgas chromatographymass spectrometry.[1] The overall chemical and structural composition is used to divide ambers into five classes.[34][35] There is also a separate classification of amber gemstones, according to the way of production.