Japanese amber

There are several amber mines from Hokkaido in the north and to Kyushu in the South at a distance of 1800 km in Japan. Together with this long distance there is a great difference of time from the former term of the Cretaceous (about 110 million years age) to the Tertiary period (about 30 million years ago). There were many mines from the archaeological point of view, but now ambers are not dug in other mines except the Kuji mine. We herein describe Kuji ambers which are dug on a small scale in the most famous mine «Kuji» in Japan.

It is reported that there was an amber road from the north to the south in the past. It is put on record that Kuji ambers of 1296 kg were transported to Kyoto in 1703 and a lot of ambers were supplied to Edo (Tokyo at present) through this amber road.

In ancient times of old tombs (the fifth and sixth centuries) Kuji ambers were transported to Kyoto and Nara which were capitals in these days and many buried jewels (magatama, etc.) were made of Kuji ambers. It was certified by analysis using infrared absorption spectrophotometer that these relics from old tombs were made of Kuji ambers.

Kuji city is located in the north at a distance of about 500 km from Tokyo. In this city now there are an amber workshop and the only amber museum in Japan. In Kuji city the stratum of a shoe-shaped structure is exposed and is about twice as older as the stratum with ambers in the Baltic Sea. This stratum is expanded from the bottom of the sea to the hill, and then to the bottom of the sea again. It contains a tolerable quantity of ambers. In 1937 and 1938 ambers of about 13 tons were dug annually.

Monster lumps of amber were dug often in the Kuji mine. A lump of amber of 19,875 kg was dug in 1927 and now is owned by a private person. Its dimensions are 40 x 40 x 25 cm. In 1941 a bigger lump was dug and contributed to the National Science Museum in Japan. Its dimensions are 40 x 23 x 23 cm and its weight is 16 kg.

This lump was broken in two and their joints are fitted perfectly. It is clear that this lump was formed as a lump of flew out resin like large lumps of Baltic and Dominican ambers. Perhaps this lump contains nothing, because many thin layers are not observed in this lump. It is reported that large lumps of 45 kg and 60 kg were dug in 1905, but they did not exist now.

A spectrum of Kuji amber is quite particular.

Clear yellow ambers are rare and a color of the most of Kuji ambers is not clear and is seemed to be orange-yellow-brown. This particular color is obtained by many little brown drops of a plane lens form. Kuji amber does not contain rainwater and moisture of any plant and contains some special substance. By heating of a small thin piece of this amber, small bubbles are ruptured at 330ºC and a camphoric odor is given out. It is supposed that kinds of trees of these ambers were special.

Striped ambers like an agate are often observed. These stripes were occurred by presence of dark-colored small bubbles one after the other.

Most of the Kuji ambers were broken by earthquakes and the pressure of mountains. In many ambers melted quartz entered later and it was crystallized at a crack. Such amber became heavily by addition of a weight of quartz and usually has stripes like a shell and white rough surfaces of rupture. In the above-mentioned lump broken in two, white quartz got covered on a white part of a surface of rupture; namely a crack of the amber was filled with a thin layer of the quartz.

Kuji ambers are discovered in stratums of sandstone and quartz. A part of these stratums directly forms the seashore and another part forms bluffs and inland hills.

A large quantity of Kuji ambers exists in a stratum with a thickness of 600 m. Mostly this stratum dips, so ambers discovered at adjacent places belong to various epochs. Most of the Kuji ambers belong to the Cretaceous (about 80 million years ago), but a small part of them belong to the Oligocene (about 30 million years ago).

Insects and other inclusions were discovered in Kuji ambers. But, regrettably, most of them are in «melted» state due to bad state of their preservation. Recently  insect inclusions has being discovered one after another and they contribute to science.

Kazuhisa Sasaki

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