Amber

Amber is fossilised tree resin prized since prehistoric times for its warm colouration, natural beauty, and ability to preserve biological inclusions. Used as a gemstone from antiquity and valued in traditional medicine, amber occurs in many regions of the world and displays considerable variation in composition and appearance. Its unique properties, including the capacity to enclose insects, pollen, and other organic material, have made it important not only in decorative arts but also in palaeobiological research.

Etymology

The English word amber derives from Arabic via Middle Persian and Medieval Latin, originally referring to ambergris, the waxy substance produced by sperm whales. By the fourteenth century this meaning entered Middle English. During the thirteenth century, Romance languages extended the term to fossil resin from the Baltic region, distinguished as ambre jaune (yellow amber), a usage adopted in English in the early fifteenth century. As ambergris declined in relevance, amber came to refer almost exclusively to the fossilised resin.
Classical Greek and Latin used terms such as ēlektron and electrum for amber, linked to words meaning “beaming” or “shining.” The modern word electricity ultimately derives from this Greek term, owing to amber’s ability to generate static charge when rubbed. In Greek mythology, amber formed from the tears of the Heliades—sisters of Phaethon—who were transformed into poplar trees.

Composition and Properties

Amber is chemically heterogeneous but primarily consists of polymerised organic compounds derived from tree resins. Its formation involves free-radical polymerisation of labdane-type diterpenes such as communic acid, communol, and biformene. Over time, heat and pressure within sediment layers drive off volatile terpenes, while isomerisation and cross-linking reactions produce a stable macromolecular structure.
Typical properties of amber include:

• Hardness: 2.0–2.5 on the Mohs scale
• Refractive index: approximately 1.516
• Relative density: between 1.06 and 1.10
• Melting point: around 250–300 °C

When heated above these temperatures, amber decomposes to produce “oil of amber,” leaving a black residue known as amber pitch or amber colophony. Dissolved in turpentine or linseed oil, this residue forms amber varnish, historically prized for its protective qualities.
Amber often contains impurities or foreign matter. Resin falling to the ground may trap soil particles, rendering the resultant amber suitable only for varnish. Bony or cloudy amber derives from dense bubble inclusions, while “black amber” is commonly a form of jet rather than true amber. Iron pyrites can impart a bluish hue. Inclusions within translucent amber can be imaged with high-resolution X-rays, allowing detailed study of ancient organisms.

Formation

For resin to fossilise as amber, it must resist decay. Many trees produce resins, but most degrade rapidly due to weathering, microbial action, and fluctuating temperatures. Fossilisation begins when resin becomes buried and shielded from such processes. Over prolonged periods, increasing pressure and temperature gradually transform resin into copal and then into true amber. European fossil resins fall broadly into two categories: Baltic ambers and those resembling resins from the Agathis group.

Varieties and Classification

Five main classes of amber are distinguished by their chemical fingerprints. Numerous varietal names have emerged over time, including allingite, beckerite, gedanite, kochenite, krantzite, and stantienite. Amber occurring in coal seams is termed resinite, while amber embedded in New Zealand coal deposits is called ambrite.
Amber exhibits a range of colours—yellow, orange, red, green, blue, and rare forms of violet or black. Transparency varies from clear to opaque. The presence of inclusions such as insects, spiders, plant fragments, or air bubbles can dramatically enhance its scientific significance and sometimes its commercial value.

Geographic Distribution and History

Amber has been collected and traded for thousands of years. Some of the richest historical deposits lie around the Baltic Sea, particularly the Sambia Peninsula and Curonian Lagoon. Ancient Greek writers such as Theophrastus and Pytheas described amber and its occurrence in northern Europe. Pliny the Elder recorded that tribes along the northern coasts harvested amber washed ashore and traded it into central Europe. The Amber Road—a well-established trade network—linked the Baltic to the Mediterranean.
Archaeological evidence shows that peoples of southern Italy, the Mycenaean world, and various Mediterranean cultures carved and traded amber long before the Roman era. In China, amber has been used since at least 200 BCE. In the nineteenth century, significant amber deposits were identified in New Jersey, marking the first notable finds in North America.

Notable Inclusions

Amber’s ability to encase organisms has made it a vital source for studying ancient ecosystems. Insects, spiders, plant fragments, feathers, and even small vertebrate remains have been preserved with extraordinary detail. These inclusions offer insights into the morphology, ecology, and evolutionary history of extinct species and environments.

Uses

Amber has long served both decorative and functional purposes:

• Jewellery: beads, pendants, cabochons, and carved pieces.
• Traditional medicine: valued historically for supposed healing and purifying properties.
• Varnish production: amber varnish and lac used in fine woodworking and instrument making.
• Scientific study: inclusions provide palaeobiological data of exceptional clarity.