Fossil resin from trees that has achieved a stable state after the loss of volatile constituents and chemical change after being in the ground, is called amber. It has been appreciated for its natural beauty and colour for a very long time. Although it is primarily used in jewellery as amber gemstone, it also has several medicinal uses.
Amber is produced by resin-bearing amber trees that thrive in a cluster in dense forests that have now become extinct. When coniferous trees are damaged, they give out a sticky substance called resin. It protects trees by sealing the gaps, breaks, or gashes in the bark, caused by chewing insects. As the resin flows on the surface of the tree, it hardens and forms a seal. Its antiseptic properties protected the tree from disease, and the stickiness gummed up the jaws of burrowing insects.
When this resin falls to the ground, it gets hardened in moist areas such as lagoons, riverbeds, and seabeds. This leads to the formation of amber material. Amber can be defined as fossilized resin that has been undisturbed for millions of years. Most of the world’s amber is at least 30 to 90 million years old.
The resin that became amber originally consisted of liquids (volatiles) such as acids, oils, and alcohols. It also contained aromatic compounds (terpenes) that cause amber’s distinctive resinous smell. Over years, the liquids evaporated from the resin, and it began to harden. The organic molecules merged to create larger ones called polymers. The hardened resin continued to polymerize and lose volatiles under the right conditions and eventually formed amber. Amber is an inert solid which has no volatiles when completely polymerized. The resins were buried in virtually oxygen-free sediments to transform into amber.
Amber is available in a wide range of different colours and in the shape of irregular rods, or nodules. Sometimes it acquires the form of stalactites and drops, retaining the manner in which it exuded from the receptacles and ducts of the injured trees. Amber flows out onto the surface of the trees but sometimes in addition to that, it also flows into hollow cavities or cracks within trees, which leads to the formation of large lumps of irregular-shaped amber.
The most common and popular colour in amber is the usual yellow-orange-brown hue that gives it the name "amber". Yellow amber is a hard fossil resin derived from evergreen trees. Amber is also found in opaque or milky-white colour (also known as “bone amber”), pale lemon yellow, brown, and even an almost black colour. Other uncommon hues of amber include red amber (also known as "cherry amber"), green amber, and blue amber.
The presence of multiple minute air bubbles in the amber causes turbidity in it. Most of the time, varied species of fossil insects and plants are also found as inclusions in amber. Those in deep translucent hues and transparent amber are considered amber gemstones.
Commonly, amber has a refractive index of 1.5–1.6, a hardness between 2.0 and 2.5 on the Mohs scale, gravity between 1.06 and 1.10, with a melting point of 250–300 °C.
Amber was collected from along the shoreline of the Baltic Sea during the prehistoric era when it got deposited by large waves and strong tides. It was also gathered from lakes and rivers where it was deposited. In current times, open cast mining on the surface of the earth and in tunnels is the way most amber is mined.
Use of Amber in DNA Analysis
Amber plays a critical role in the DNA analysis of several prehistoric insects and animal species. As the tree resin fell on the surface of trees, sometimes insects and plants got trapped in this resin. Since amber is transparent, these trapped insects and plants are clearly visible even after the resin has fossilized into amber.
Many times, animals as large as frogs and lizards were trapped in the resin. As the bodies of these insects, animals, and plants are well preserved in amber, sometimes it is possible to extract their DNA. By studying the DNA of these trapped creatures and plants from prehistoric times, scientists have been able to learn a lot about those times.