http://www.thefossilforum.com/index.php?/gallery/image/55506-tiger-mountain-amber-tukwila-fmrenton-fm-boundary-middle-to-late-eocene/Tiger Mountain Amber (Tukwila Fm./Renton Fm. [Boundary], Middle to Late Eocene)

- Subjects:
Three exceptional specimens of amber, recovered from exposures on Tiger Mountain, Washington State; this is the first of two videos detailing the specimens' natural fluorescent and phosphorescent responses: 140 lumen LED light (yellow phosphor) was used in this entry. All were prepared by hand using a diamond needle file, 240 to 3,000 grit SiC sandpaper, and chromium oxide (ZAM compound) on a Selvyt microfiber cloth.

- Brief Description of Deposit:
Tiger Mountain amber occurs in lignitic coal seams, mainly contained within two Geologic Formations, namely the Tukwila and Renton (along their boundary); there is also a third, the aptly-named Tiger Mountain Fm., that hosts amber-bearing coal, though not to such a degree as the former two. The Tiger Mountain Fm. (roughly 2,000 ft. in depth) underlies and is inter-bedded with the younger Tukwila Fm., while the Tukwila Fm. is overlain by the Renton Fm.: the amber-bearing coal contained within the three Formations spans a geologic timescale ranging from Middle to Late Eocene in age (~41.3-33.9 Ma).

- About Amber Fluorescence:
The light blue fluorescence emitted by some of this amber upon exposure to LED and sunlight, bears a remarkable resemblance in color and intensity to that of blue Dominican amber. Various aromatic hydrocarbons, naturally contained within the blue variety of amber, are responsible for this fluorescence. Blue amber is commercially mined from three major sources: Sumatra (Indonesia), the Dominican Republic, and limited production from Chiapas (Mexico) deposits.

Source: https://file.dnr.wa.gov/publications/ger_ri21_strat_eocene_king_co.pdf