Frozen in Time: Ancient, Long-Fingered Lizard Trapped in Amber
In a case worthy of Sherlock Holmes, researchers are trying to figure out exactly when and where in the world a long-fingered lizard got trapped in the sticky sap of a tree.
Over time, that sap, or tree resin turned into amber, preserving the lizard's remains, including its textured skin. This unique lizard-amber block somehow came into the possession of a man who donated it to the Miller Museum of Geology at Queen's University in Ontario, Canada, in the 1980s, but the man didn't report the artifact's age or provenance.
"The man who donated it died, unfortunately," said Ellen Handyside, an undergraduate student studying geological engineering at Queen's University, who is leading the research into the amber-encased lizard. "We are really starting from scratch" in determining its history, she said
Then, she and her colleagues analyzed the chemical composition of the small, 4.7-inch-long (12 centimeters) piece of amber, learning two key facts: First, the amber was real, meaning "it proved it wasn't a fake," an important point given that so little was known about the sample, Handyside told Live Science. And second, "we found it did match up quite well to a Dominican [amber] sample," although the results weren't conclusive, she said.
Color Phenomena of Blue Amber by GIA
The greenish blue color observed in some amber from the Dominican Republic and Indonesia is actually fluorescence stimulated by ultraviolet (UV) light. A previous study described the color as iridescence over a yellow background, but it is in fact a surface fluorescence. Since this amber can be considered a long-wavelength pass filter with a half-pass wavelength at about 530 nm in its spectral transmittance, it does not transmit either UV or short-wave visible light. As this material completely absorbs light in the UV range and strongly absorbs light in the short-wave visible range, the stimulated blue color is confined exclusively to the surface. The amber from this study also showed the Usambara effect, the phenomenon in which color varies with the path length of light through a sample.
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. Amber 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. This variety comes from the resin of the extinct tree species (Iturralde-Vinent and MacPhee, 1996; Poinar and Poinar, 1999). According to Iturralde-Vinent and MacPhee (1996), most Dominican amber occurs in two zones: north of Santiago de los Caballeros (the “northern area”) and northeast of Santo Domingo (the “eastern area”). Although resinites of different ages exist, available biostratigraphic and paleogeographic data suggest that the main amber deposits in the Dominican Republic (including those famous for yielding biological inclusions) were formed in a single sedimentary basin during the late Early Miocene through early Middle Miocene (15 to 20 million years ago). There is little evidence of extensive reworking or redeposition of the ambers. Before the studies of Iturralde-Vinent and MacPhee (1996), amber from the northern area was thought to have formed during the Early Eocene to Early Miocene epochs (Baroni-Urbani and Saunders, 1982; Lambert et al., 1985; Poinar and Cannatella, 1987; Grimaldi, 1996), while published estimates for the eastern area ranged from the Cretaceous to Holocene epochs (Burleigh and Whalley, 1983; Poinar and Cannatella, 1987; Grimaldi, 1996). Bellani et al. (2005) studied blue amber from the Dominican Republic and identified the aromatic hydrocarbon component perylene as the source of the UV-stimulated fluorescence emission in the visible wavelength range from 430 to 530 nm, resulting in the observed greenish blue color. They also described the blue color as iridescence under natural daylight or daylight-equivalent lighting. Iridescence is an optical phenomenon in which a surface appears to shift color as the viewing angle or angle of illumination changes (Nassau, 1983). Although most iridescence is caused by interference, Liu et al. (1999b) found that in pearls and shells it results from diffraction. Each layer of shell and pearl is optically heterogeneous. Light is strongly diffused as it passes through the layers, causing the milky white color observed. The diffused light cannot produce interference to cause the iridescence color. For this to happen, each layer would have to be optically uniform and have a thickness on the order of visible-light wavelengths. UV fluorescence is also known to cause significant visible color change in some diamonds. Strong UV fluorescence under daylight caused such an effect in the 56.07 ct Tavernier diamond (Liu et al., 1998). The UV fluorescence changed the entire diamond’s bodycolor from light brown under incandescent light to light pink under daylight. The phenomenon by which bodycolor varies with a gemstone’s thickness is called the Usambara effect. Liu et al. (1999a) determined that this color variation is caused by the hue angle change corresponding with the path length of light through a gem material. This article presents the color phenomena of blue amber from the Dominican Republic and Indonesia. Fluorescence and photoluminescence were measured at room temperature to show the characteristic features. As a result, we found that the amber’s greenish blue color is only superficial. By calculating the colorimetric data at different depths within a sample, we determined that the hue angle changed with depth, an indication of the Usambara effect in blue amber.