Gem News International Gems & Gemology, Fall 2022, Vol. 58, No. 3

Pressed Amber Imitation for “Root Amber”

Shu-Hong Lin, Tsung-Ying Yang, Kai-Yun Huang, and Yu-Shan Chou

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Dark brown “root amber” beads exhibit light yellow creamy swirls.
 
 
Figure 1. This bracelet containing 12 mm beads was submitted as “root amber.” Photo by Tsung-Ying Yang.

Root amber, a commercial variety of burmite (amber from northern Myanmar), is popular in the Taiwanese market. As the name suggests, root amber resembles tree roots and usually has a dark brown to light yellow color with creamy swirls caused by the mixing of fine calcite particles and resin during the sedimentation of the amber (Y. Wang, Amber Gemology, China University of Geosciences Press, Beijing, 2018, p. 244).

Pressed amber (top) appears less homogeneous than natural root amber (bottom).
 
 
Figure 2. Pressed amber imitations and natural root amber. Under white light, the pressed amber (A) appeared less homogeneous than natural root amber (C). Granular structure of the pressed amber (B) revealed under long-wave ultraviolet light, whereas natural root amber showed relatively even fluorescence (D) under the same long-wave UV lighting. Photomicrographs by Kai-Yun Huang; field of view 4.23 mm.

Recently, a bracelet was submitted to Taiwan Union Lab of Gem Research (TULAB) as root amber (figure 1). This bracelet consisted of a string of dark brown beads with light yellow creamy swirls. The refractive index of these beads was about 1.54 by spot reading, which was consistent with the RI of amber, and the beads showed uneven medium blue to faint yellow fluorescence under long-wave UV light. Microscopic observation of the beads revealed slight differences from natural root amber. First, the yellow swirls appeared to have a coarse texture rather than smooth. Second, the brown regions seemed to show a vaguely granular structure. The beads were further investigated under a microscope with long-wave UV illumination and compared with those of natural root amber. The results of fluorescence microscopy revealed that these regions did, in fact, show a granular structure with particle sizes ranging from tens to hundreds of microns, while the natural root amber appeared relatively fine-grained and homogeneous under the same lighting (figure 2). Raman spectroscopic analysis and comparison with both the RRUFF database and the internal amber references compiled by TULAB confirmed that these beads were made of amber and calcite particles (figure 3). Previous studies also pointed out that the strongest peaks at 1645 and 1450 cm–1 may respectively be assigned to ν(C=C) and δ(CH2) modes in fossil resin (R.H. Brody et al., “A study of amber and copal samples using FT-Raman spectroscopy,” Spectrochimica Acta Part A, Vol. 57, No. 6, 2001, pp. 1325–1338). To summarize, the amber bracelet should be defined as an imitation—specifically, a pressed amber mixed with calcite powder during the manufacturing process.

Raman spectra of calcite and amber references compared with the “root amber” bead.
 
 
Figure 3. Raman spectra comparisons between the spectrum of the bead, amber reference (TULAB), and that of calcite from the RRUFF database suggested that the bead consisted of calcite and amber. The peaks at 1645 and 1450 cm–1 may be assigned respectively to ν(C=C) and δ(CH2) modes in fossil resin. The stacked spectra are baseline-corrected and normalized.

Although pressed amber has long existed in the trade, the addition of calcite powder made this sample a better imitation of natural root amber and more difficult to distinguish by standard gemological testing. The best identification method for such an imitation is observation with fluorescence microscopy.

Shu-Hong Lin is chief gemologist, and Tsung-Ying Yang, Kai-Yun Huang, and Yu-Shan Chou are gemologists, at Taiwan Union Lab of Gem Research in Taipei.