Amber from the Mesozoic Era, most common in Cretaceous deposits, occurs in Japan, Taimir, Switzerland, Lebanon, Alaska, New Jersey and elsewhere. Amber that is earlier than the Tertiary Period is regarded as originating only from conifers. An example is New Jersey amber, exhibiting various shades of colour that are redder and darker than Baltic amber. Alaskan amber, on the other hand, is unusually transparent and intensely coloured, displaying a range of tones from honey-yellow to black. Japanese amber often has a pleasant caramel colour. It occurs together with marine fossils and is about 85 million years old. Located on Russia's Taimir Peninsula is possibly the world's largest Cretaceous amber deposit, while Lebanon has one of the oldest occurrences of amber, from about 120-130 million years ago.
Gemologists are only interested in a few forms of amber that have served as raw material for jewellery in different historical periods. These were all formed during the Tertiary: Baltic amber (succinite), Romanian amber (rumenite), Sicilian amber (simetite), Burmese amber (burmite), as well as amber from Mexico and the Dominican Republic. Succinite characteristically displays honey-coloured shades of yellow, and is unique in having a very high content of succinic acid: 2-8%. The term rumenite was introduced by Otto Helm in 1891 for the red-brown amber from the Buzeu Valley. It is not really correct to apply the term to the other forms of amber from Romania, since they are mostly pale yellow and exhibit marked internal cracking. The name simetite comes from the River Simeto, along whose banks Sicilian amber may be found. This amber, often fluorescent and showing an unusual range of colours, has nowadays become very rare. Burmite varies in colour from a rich brown to a watery yellowish tint (sherry-coloured), but intensive yellows and bone colours never occur. Most highly valued is cherry-red burmite. Often noted in the literature is the property of burmite of fluorescing in daylight with a blue-green or violet colour. Although Dominican amber is mentioned already by Columbus, it has become more widely known only during the past 20 years. The recently discovered sources are quite rich and provide comparatively large pieces. It is the softest form of amber, but in terms of other properties, Dominican amber resembles simetite.