Amber won't fit a giraffe, but it'll fit your wood floor.

Amber and pearls are unique among gems-they belong to "organic gems", that is to say, they are mainly composed of organic matter.

In the history of chemistry, the original definition of "organic matter" is its literal meaning-substances and their derivatives that can only be synthesized by organisms. Pearl, for example, is the secretion of some bivalve molluscs, while amber is a fossil of resin secreted by some trees.

Amber wrapped with all kinds of bugs. Picture: Didier Descouens / wikipedia

According to the current research conclusions, there are many kinds of trees that can form amber, most of which may be gymnosperms (such as pine, cypress, fir), but some angiosperms can also form amber. Among them, the famous Dominica amber (and similar American amber such as Mexican amber) has been confirmed to be fossilized from the resin of an extinct legume plant Hymenaea protera (or Dominica amber beans). Although Dominica amber beans are extinct, scientists have found that they are closely related to another living plant, Hymenaea verrucosa.

Which is better to secrete resin?

This extant amber bean belongs to the genus Hymenaea, so named because each leaf is made up of a pair of leaflets, like twin sisters. Thirteen of the 14 living species of the genus Leguminosae are still native to tropical America, except for the amber bean most closely related to Dominica, which is found in East Africa. Because of this geographical difference, some scholars have put it into a separate genus-Trachylobium.

Note that each leaf consists of a pair of leaflets. Picture: Dinesh Valke / wikipedia

The intermittent geographical distribution of the genus Phaseolus in America-East Africa is not difficult to explain. At the time of the origin of this genus, America and Africa had just split from a larger ancient continent of Gondwana, so there are plants of this genus on both continents. With the continuous expansion of the Atlantic Ocean and the growing distance between America and Africa, the genus Twin developed independently on both sides, the American "pedigree" was more prosperous, the African "pedigree" was more miserable, and finally formed today's trans-oceanic geographical distribution pattern.

Look for evidence in fossils

How do scientists confirm that amber beans are closely related to Dominica amber beans? First of all, on the preserved leaf fossils of Dominica amber beans, people can see clear veins similar to those of living amber beans. Although in general plant identification, leaves can identify plants more quickly than flowers and fruits, for paleobotanists, leaves are very important organs and contain rich information in the morphology of leaf veins.

The leaf of Dominica amber bean is fossilized. The fourth picture shows enlarged veins. Photo: George O. Poinaret al./Experientia (2005)

Secondly, although most of the DNA in the cells of an ancient plant was degraded 30 to 40 million years ago, paleobotanists managed to extract some chloroplast DNA fragments from them, and compared them with existing tree species after sequencing, and finally determined their genetic relationship from both morphological and molecular aspects.

After tens of millions of years of evolution, Twin Leaf Bean species are still famous for secreting resin. Twin-leaf bean resin is traditionally classified as a class of resins called copal. In addition to the genus Leguminosae, the olive resin Protium copal is also the source of this kind of resin. There have been many translations of the word copal in history, such as Koba fat, Kobo fat, bone fat, and so on. Of course, the most amazing one is Wang Gu [Wang Ba] fat, for which two words that cannot be typed by ordinary input methods have been created.

Resin is flowing from the trunk of the amber beans. VE McCoyet al./ScienceDirect (2017)

In addition to amber, you can also paint.

The confusion of Koba fat in translation shows that the Chinese are strange to it. According to the records of Chinese Flora, two species of Twin Leaf Bean are cultivated as cash crops in South China and Taiwan, namely, H. courbaril and Amber Bean (called "verrucous Twin Leaf Bean" in Chinese Flora). However, the cultivation belongs to cultivation, and in the end, it has not been promoted into widely planted economic tree species.

So what's the use of this kind of Koba fat? It turns out that it is an important ingredient of varnish. Varnishes are made by dissolving solutes such as resin in liquid volatile oily solvents such as turpentine. Apply the varnish evenly to the surface of the object, the oily solvent gradually volatilizes, and the solute such as resin dries gradually, "solidifying" into a hard, impervious and glossy layer, which not only protects the surface of the object below, but also looks beautiful.

The kitchen wood floor with three layers of varnish is waterproof and bright. Picture: avlxyz / flickr

In the 19th century, Westerners found that the varnish made of amber bean resin had excellent properties and was especially suitable for use on wood, so it was imported in large quantities from Africa, especially Zanzibar Island in Tanzania, which is the largest producer of amber beans. It was not until the 20th century that as synthetic chemical paints began to be put into use, the demand for Kobar varnishes continued to decrease. In China, tung oil and lacquer are two kinds of varnish-like paints that have been widely used since ancient times, and China has entered the era of chemical lacquer before Koba grease varnish can replace them. No wonder we are new to amber beans and Koba grease varnishes today.

However, in the world of gems, Koba fat is still famous because some "subfossils" of Koba fat, which are buried only a few million years ago, are often sold as fully fossilized amber. so that how to identify real amber and fake amber has become a necessary lesson for anyone who wants to play with or invest in organic fossils-just like people who like organic food. We should also pay attention to whether they eat real organic food or fake organic food.

This article is the 234th article in the fourth year of the species Calendar, from the author of the species Calendar @ Liu.

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Mimosa Leguminosae