What Causes the Color of Blue Amber

Blue Amber

Blue amber is a rare variety of amber that exhibits a blue coloration when viewed under ultraviolet light.

Blue amber is found primarily in the Dominican Republic, with smaller deposits in Mexico and Indonesia. The blue color is caused by the presence of the aromatic hydrocarbon perylene, which fluoresces blue when excited by ultraviolet light.

Amber is fossilized tree resin used for jewelry, decoration, medicine, and perfume. Specimens with inclusions of insects and plants are of great scientific significance and highly esteemed by collectors. 

Blue Amber
Blue Amber

Amber color is usually yellow to brown, and some specimens display red to brownish red or reddish brown colors. Blue amber is rare, found mainly in the Dominican Republic with some production from Indonesia and Mexico.

Causes of Blue Amber coloration

The blue color of Dominican amber is caused by special molecules called aromatic hydrocarbons. These molecules absorb ultraviolet light and then emit it as blue light, making the amber glow blue under UV light. The most important of these molecules is perylene, but other aromatic hydrocarbons like fluoranthene and retene can also contribute to the blue color.

Natural Blue Amber
Dominican blue amber.

The blue fluorescence is not uniform throughout the amber. It is strongest near the surface where UV light penetrates easily, and it gets weaker as the light travels deeper into the amber. This is because the light is absorbed and scattered by other molecules in the amber. This creates a captivating interplay of blue and yellow/orange tones, especially noticeable in thicker pieces.

The size and distribution of the aromatic hydrocarbons in the amber also affect the color. Larger, more concentrated clusters of these molecules tend to produce a stronger, deeper blue, while smaller, scattered clusters might result in a lighter, more ethereal blue.

Recently, optical absorption, fluorescence and time-resolved fluorescence measurements in Dominican ambers have been reported. These studies show that the "blue" variety reveals an intense fluorescence emission in the visible wavelength region, between 430 and 530 nm, with spectral features typical of aromatic hydrocarbons. On the contrary, the Dominican "red" and "yellow" amber varieties have a much weaker and featureless emission, although still do have a certain fluorescence. The process in blue amber is surprisingly similar to phosphor.

Although there are several theories about the origin of Dominican blue amber, there is a great probability that it owes its existence to ingredients such as anthracene as a result of 'incomplete combustion' due to forest fires among the extinct species Hymenaea protera trees about 25 to 40 million years ago.

Blue Amber
Blue amber from Indonesia. photo By Chille Maulidhaa

Properties of blue amber

  • Color: Blue amber exhibits a range of blue hues, from light blue to deep blue.
  • Transparency: Blue amber can be transparent, translucent, or opaque.
  • Fluorescence: Blue amber fluoresces a bright blue color under ultraviolet light.
  • Hardness: Blue amber has a hardness of 2-2.5 on the Mohs scale of mineral hardness.
  • Density: Blue amber has a density of 1.05-1.10 g/cm³.

Additional information about blue amber

  • Blue amber is not as hard as other types of amber, so it is more susceptible to scratches and damage.
  • Blue amber is a relatively new discovery. It was not until the 1990s that it was first recognized as a distinct variety of amber.
  • Blue amber, also known as Dominican amber or Baltic amber.

See also: 
Pictures: Types of Amber
The Eight Most Incredible Fossils Preserved In Amber
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